LASS and Hollywood Winds would set you back around 1.5K and you wouldn't be able to run the full LASS on your current system. You could run the ensemble sections but that's like having one hand tied behind your back. You'd be better served by getting a broader based library like EW Gold to start with and work up from there, at least you'd have more than strings and woodwinds, you really need good brass and percussion these days as well. I know matto has had several placements with orchestral pieces he has written using Gold exclusively, he just writes to the strengths of his samples and avoids the weak spots and fills those in as he can, which is a sound strategy, IMO.
That's my 2c as far as getting involved in the orchestral realm. I think you have enough right now to make some great noise. Maybe going deeper into those instruments (and you know how deep Omnisphere is) is a strategy to consider, rather than broadening out. Of course, it's all up to you in the end, I'm happy to throw out options all day long!
You're doing the right thing by weighing the options. Selfishly, I hope to shake your hand and clink glasses with you come November.


Cheers!
Mazz
EDIT: Actually a couple more things come to mind:
I have very little acoustic treatment in my studio, just 3 2X4 panels from Ready Acoustics (around 200 bucks for 3), a futon and some bookshelves. My music has had some decent placements, so I can say that if you learn your room and your speakers, you can do OK with minimal treatments. It's always nice to have it, but it's not 100% necessary at this stage of the game unless you have the money laying around anyway.

Kontakt and Logic already have some orchestral instruments in them and the strings in Omnisphere can do some very nice things as well. You wouldn't be able to do everything you may hear in your head, but you have a good basic kit there and if you use the best sounds and make music with those, you just might be able to pull off some orchestral stuff, particularly if you are blending in rock/tronica type stuff as well. Use what you already have to it's fullest and you'll have a lot more experience when you graduate to the next level of library.