I thought I'd share a Keyboard Magazine "Orchestral Sounds Roundup" that I've found useful:
http://www.keyboardmag.co...l-sounds-roundup/48460
 

My thoughts.:
I have EWQL HO Gold and see my specs in my sig. I run it without issue with perhaps 40 - 60 tracks. Keep in mind that the subscription HO is the Gold version (which I have). The Platinum version would indeed strain your PC, while Gold may be OK if your specs are similar to mine. The main difference is that the Platinum version has 16 and 24 bit samples with multiple mic positions. The Gold version has 16 bit samples and one mic position. This piece was written with HO Gold and at the time I had 16 GB RAM:
https://soundcloud.com/dave-ranck/the-song-of-llorienne
Listen to the violins and violas in the second half of the second verse.
 
#1: I’m on Windows 10 and have no issues yet. :-)
#2: See my comments above.
#3: It is not simple to learn but very rewarding. You need to be willing to study the manual. Of course, good orchestration techniques are required to make any library sound better. Groove3.com has a nice training series on orchestration and music theory.
#4: You need fast hard drives. SSD is best but my 7200 drives work OK for me. You can freeze tracks if needed, but I usually have more issues with certain Kontakt libraries than I do with Play. YMMV.

EW makes a great effort with their sales to where everyone can buy their products. 
EWQLO Gold - can be had for $250 if you wait.
Hollywood Silver series $100-$150 for each module.
 
I also like VSL. Their player is amazing. You can buy a la cart.
 
If you have Kontakt - the bundled orchestras sounds are underrated. These are the old VSL libraries. Check out the choir.
 
 Some good advice is to use one and know it well before jumping to something else. There are people who can make GPO sound great and also that free Sonatina library.  If you don't know what you are doing in orchestra, better tools will not make you better.

I STILL have my original East West SO Silver Kompakt Edition from Native Instruments...

And it STILL works...