I can only speak for myself of course, but I don't see the benefit in using both MIR Pro 24 and MIRx in tandem. What's the point? To me, it would make more sense to go all MIRx. It gives you a uniform sound and doesn't get in the way. That's what I love about it. It sounds good and lets me write music, instead of being held up by technicalities that ultimately bore me.
If you really perceive some kind of difference between MIRx and the Pro 24 presets, using both would mean having different sounding "room tones" in the same template, which kind of defeats the point of MIR/MIRx in the first place. Or you would end up having "A list" and "B list" instruments in your template. I understand the economics of it, but it's a strange mentality to work with, for me personally. And it's a kind of a non-streamlined mishmash.
I believe that having everything sitting in the same room and sounding the same is most important and has the greatest effect on the perception of authenticity, even if the means of creating the room are simple (e.g. a simple algo verb bus). So, personally, if the 24 channels of the MIR Pro 24 don't suffice, I think I'd rather save up for a full MIR Pro. Or just go with a simpler solution/stick to what I have.
My personal priority would put additional libraries and articulations on top. I think that's where the music ultimately comes from. It has the greatest effect on the writing, the inspiration, creative decisions and the detail of expression IMO. The rest is "just" tools.
For example, you mentioned VE Pro: as long as you're staying on one machine, I don't see it as a priority. What for? I know people who use a bunch of VSL stuff in addition to ridiculous amounts of GBs of other sample libraries - an obscene amount of samples - and they want or have to cram it all into a single template that consists of hundreds upon hundreds of tracks. Those guys obviously need a slave computer and VE Pro to manage all that.
I don't want that, luckily I don't need it and I never got the appeal. I try to keep things as simple and compact as possible, and my basic template is less than 100 tracks. I don't want these things to become too distracting and too fiddly, because I feel it's harmful to the creative process. As long as you're staying on one machine - which is absolutely viable, especially if you're working with the SEs - I don't see a big need for VE Pro.
Then the Vienna Suite: I had demoed it, and I worked on a project where it got used in the post production quite a bit and I've seen it in action. It's a great product, I especially really liked the reverbs and the compressor. But in the end, it's a collection of audio plug-ins. You have those in Cubase. It's not like you're in dire need of acquiring EQs, compressors and reverbs because you don't have anything to work with.
The stuff that's included in Cubase is good. The EQ is absolutely fine, the compressor does what it's supposed to, even the new algo reverb is really nice. And you have the MIRx bundle on top of that. One can always expand in this department later on along the way, and the Vienna Suite can be a great complement, but for someone who's on a budget and already has proper processing tools at their disposal, I wouldn't view it as a priority either.
It most certainly isn't gonna elevate your music to an audibly higher level at this point. In fact, I'd argue that any hobbyist should first spend a lot of time researching, practicing and learning to use good stock plug-ins like the ones Cubase comes with before spending money on third-party software. Stuff like EQ, compression etc., is really something one needs to learn to listen to and work with first, in order to even be able to make educated judgements and choices on additional products.
So personally, I'd prioritise acquiring additional sounds. The SE2 bundle makes a lot of sense if you're working with SE1+. There's also a lot of great expansion options with the download instruments. As far as software and processing goes, if you really like what MIR has to offer and have a lot of fun working with that, I'd rather save up for the "big" MIR Pro before spending limited funds on VE Pro or Vienna Suite. I think it just has more to offer in your particular situation.