From how you describe your music SE would probably work really well for you. The cube is really for classical composers who are writing for anything from chamber ensembles to full orchestras. Plus, they usually go onto buy the extended version of the libraries in order to get all of the additional articulations, which I don't think you would use.
You might want to consider getting the Standard Version of Appassionata Strings I, instead of Volume 3 of the SE. I have a feeling you would use Appassionata a lot, and they are basicly the same price. That is unless you need muted versions of your strings. Be sure to listen to the Appassionata Strings demos to see if that's a string sound you would use. (I know for me, it's going to be my next VSL purchase.)
Once you get one or more VSL libraries, I'd try out MIRx. I'm pretty sure you can demo it for free. It's so simple to use and sounds amazing. There's a good demo of it used with just SE Vol 1 http://www.vsl.co.at/en/211/442/478/449/287.htm.
One thing to keep in mind with MIRx, is that it can only be used on VSL instruments. You can't use it as a plug-in in your DAW to run it on other companies virtual instruments or audio tracks. (Someone correct me if I'm wrong)
The Vienna Suite is a great collection of effects for the classical composer. I really like it because there are eq and compressor settings for (I believe) every VSL instrument. Which makes getting a good sound very easy. However, it sounds like you already have a lot of similiar effects, so it may not be worth it for you to buy the Suite. I belive you can demo it as well though.
One thing to keep in mind is that all of the VSL instruments are sampled "dry." That is no reverb, and they can sound rather flat without effects. This was done on purpose, so that you can put them into any mix that you want and you aren't stuck with one specific sound. You'll want to use either MIRx or another reverb on them to get them to sound natural. (The Vienna Instruments Player that you get free when you buy an instrument includes a descent built in reverb.)
Michael