Hey LuCsa,
This is going to be a "little" of a long read, but perhaps you find it worth your time. Maybe lot of the info here you already know, but indulge me and hopefully I can share something useful to you.
I have done much research on what to get and how to assemble a music computer. I just finished assembling my temporary workstation based around Windows 10 Pro. I use Cubase 8.5.20 with Albion and CineSamples (for now). Albion, especially, is very resource hungry. Spitfire Audio makes top noch samples, but they come with a cost and it's not just the price tag, but it's also your CPU, RAM and storage capabilities.
Anyways, allow me to give you my two cents of what I found out to be helpful and necessary so far. But before that, you need to understand (and maybe you already do) that there are things you can allow yourself to cheap out on and other that you just cannot. With that being said, here we go.
1- CPU and Storage Solution is your new best friend. A musician needs to be very familiar, especially nowadays when sequencing has become the main way to make music for media, with the concepts of Multi-threading, Core count, base-clock speed, PCIe lanes, Spinning platter HDDs, Flash storage (SSDs) solution, nVME (PCIe and M.2 storage) solution and, finally, RAID methodology.
This may sound very overwelming already, but I promise you that it sounds fancier than it actually is. The CPU and the Storage Solution are your two new best friends because they belong to the family of "cannot cheap out on". Sometimes a 500 dollars more expensive CPU can very well be the difference between a on-time stems delivery and a late stems delivery. There are two sides of a CPU purpose in Music composition and sequencing: Core Count and Base Clock Speed. There is also Turbo-Boosting, but we get there later.
a. Core-Count is essentially the amount of Cores the processor has. PHYSICAL cores, not logical cores. What's the difference? Well, when we talk about physical cores we refer to the actual physical amount of chips contained in the Processor. (e.g. Intel Xeon E5-2697 V4 18-Cores, 36 Threads) You see, in this example you have 18 Physical Cores and 36 threads. When talking about Thread we are talking about Logical Cores. So, you can think of it as in "there are 2 Logical Cores per Physical Core". Now this particular processor has a Base-clock speed of 2.3 Ghz, but it Turbo-boosts up to 3.6Ghz (this is an insane CPU, which I am actually after right now). This means that, when idle or with very very small workload, the motherboard floats this Processor voltage to a maximum of 2.3 2.4 ghz. But when under load, the motherboard allows the voltage to bump up and give more current to the CPU, allowing it to jump to what is called Turbo-Boost mode, which brings it to 3.6Ghz, allowing to calculate and move information much much faster.
SO, how does this apply to you? Well, you want the processor that gives you the maximum amount of cores with the highest turbo-boost clock speed. This way you have 2 advantages (and barely no drawbacks) 1- You have lot's of cores to store your tasking calculations (DAWs usually need more than four cores to function to top functionality) and you have a high clock speed which reduces latency when playing-back or recording live.
b. When it comes to storage solution, there should not be any compromises. Your storage needs to be fast, and by fast I mean, forget HDDs (Spinning Platter Disk) of any sorts. No matter if you RAID 0 them, they will be far too slow for the sample libraries we have nowadays. Before this Windows machine, I owned a MacPro 6-Cores for about 4 years and the only SDD was the OS...dark times. They are noisier, slower and break easier because of the moving parts and the machanical friction. They function much better as long term storage and backup devices, where they have to move data araound as less as possible.
Anyways, longs story short, look from SSD foreward, and yes, prices increase a little, but today the most espensive 250GB SSD you find is made by Samsung (850 EVO) and it floats around $80 bucks, not too bad, cosindering that you can shove in there a few sample libraries.
Now, to understand this further, your SSDs are responsible for how fast and how well your data stream is from disk to DAW, in other words, from the moment you selct the instrument to the moment all the samples are loaded, your processor, RAM and disk are working very hard. However, if you cut that time in half (or more) all those componets work way less to load that instrument, and they can focus their strength on other parts of the software. This will allow your to stream from disk faster and with less waste of resources from all the other components.
Another solution for your storage (albeit far more expensive) is PCIe Storage, that uses nVME technology. An example of that is the renouned Intel 750 Series, this PCIe ssd is extremely fast, reaching, sometimes, the reading spead of 1.5 - 1.7GB per second. Blazing fast. However, a 400GB model is still around $350.
The nVME technology, which is simply a faster communication, smaller size and more efficient use of the storage cells inside the SSD, is also found in the M.2 SSDs, and there are 2 types (SATA M.2 and PCIe M.2) The PCIe ones being faster than PCIe SSDs, btw. Usually people deploy them as OS drives, tha way the softwares and the OS load snappier and without much trouble. Generally you want to look at at PCIe 4x (4 lanes) M.2, which, most motherboards support nowadays. However the drawback of this M.2 is that is going to desable one of your PCIe slots to dedicate to itself. So when in the BIOS you enable the M.2 to run in PCIe 4x mode, you are sacrifying one of your espansion slots. No, don't worry, it's not the first one where you Graphic Card usually sits.
c. LANES. Something that us, workstation users, need to be aware. The reason why is because we tend to be the most users and abusers of expansion slots. For gamers, all you need is...love..NO! All you need is the graphics card slot and, most of the time, that's about it. But for us, we sometimes want a workstation Graphic Card, USB 3.0 PCIe expansion cards, Wired Network Cards over PCIe (for further LAN and ethernet connectivity), red rocket cards, Pro Tools cards, storage, ect. So they run out pretty fast. Now, WARNING! lanes are not equivalent to the amount of PCIe slots you have on board, they are calculated out of each and intividual peripheral, that's why it's tricky. A Enthusiast, gaming graphics card can function on 16x (16 lanes) or 8 lanes, thus occupying, of course, 16x or 8x. A good processor has around 40 lanes of capacity, which means that you can shove in a total of 40 lanes worth of expansions. The M.2 will take 4x, the PCIe SSD will take between 4x and 8x (more likely 8x), the graphics card will take between 8x and 16x, each SSD or HDD plugged in through SATA connection will take it's share of those lanes (although much less significant, but still worth considering). So, with a processor that can only support 18-24 lanes, you won't go far on a Workstation Computer. However, if you opt for a Haswell E or EP, Bradwell E or EP (E being the enthusiast grade and EP being the Xeons) you should be okay, although there are some in these families (the cheaper ones) that have half the lane support. Always check manufacture websites to verify how many lanes are supported, that way, when you slap in an expansion card and it seams very slow or sometimes even not functioning correctly at all, you know why.
2- RAM. Now this is something that is most commonly thought to be the cause of fastness or slowness of yout Workstation. While that is true to a certain extent, it is also false. RAM dosen't impact "speed" if your sistem, it just impacts how well, how much and how fast the informations that are needed the most in that particular situation, are handled and transfered between storage to application. For instance, if I have a session where I have 2 fully loaded instruments, (let's say one instance of Kontakt 5 with the AlbionONE Strings - around 230MB - and the second another Kontakt 5 instance of CineStrings 1 Violins True Legato - 400MB -) approximately 630MB of your, hipotetically, 4GB of RAM are accupied by the instruments, and they remain there because the CPU is telling the RAM to keep 'em there for fast recall, so those files travel from disk to RAM and stagnate there till you shut down your DAW or your PC altogether. You can see that as you increase the instruments count, your RAM will have to handle more and more information. So, the more you have it, the better for Workstation purposes.
I personally recommend DDR4, all the way and not less than 32GB, running at no slower than 2133MHz.
Many people here may not agree with this, and I can see why. But, again, these are my two cents. The amount of RAM really does depend on how many VST you are going to use and how heavy they are. If you use mainly Synths, you will be able to get away with 16GB or even 8GB, no sweat. But as soon as you start delving in the realm of Vienna, Spitfire Audio, CineSamples, ProjectSAM, 8DIO, so on and so forth, you might want to consider upping your game.
3- Motherboards are a little less of a concern, although, if you want to be ideal, they can be considered and they do make a difference. I usually advice two types of motherboards for workstation purposes:
a. Gaming MoBos are usually very well built and sturdy. They tend to have a good amount of connectivity and they, most importantly, support a large variety of high-end processors, including Xeons (if you go with the X-99 chipset). Skylakes, while very powerful for gaming and video rendering, are not really indicated for music production, althoug my i7-6700 3.4Ghz is not really bad, it's just a 4-Cores 8 threads so it does struggle a little bit when I have 40-60 instruments playing at the same time.
b. Workstation Grade MoBos are the IDEAL solution. Anything that has the letters WS or WS-E in front is bound to give you the most solidity with your components. They are just built for heavy-duty, task intensive and professional work. In the build I am planning to put together, hopefully, in the next few months, the MoBo I chose is the ASRock WS-E X-99 model. This thing as 7 PCIe expansion slots all 16x, 8 slots for RAM dims, chockers that are second to none and plenty of features.
As I mentioned before, another point to consider when choosing a motherboard for workstation purposes, is wheather you're going to get an X-99 chipset or a Skylake Chipset. Apparently, and I don't have benchmarks on this so I'm just speaking out of work of mouth, the X-99 is a much more reliable and solid chipset for professional work.
I think this covers it all and, again, hopefully this has not bored you but tought you something you didn't know that can turn out to be useful for you in the future.
Best
Lorenzo