The best piano is Synthogy's Ivory, Not only does it play beautifully, and sound great but has some great less "real" patches too and lovely sounding reverbs.
I'd say with your budget get Komplete 7, and then add on extra libraries as you see fit, LASS, east west or VSL for instance.
Other really useful software is spectrasonics, RMX, Trillian and omnisphere as with these you'll have your, loops/beats, bass, synths and pads/textures pretty much covered. for great real sounding drums, addictive drums are great sounding and MUCH lighter on rescources than DFH etc.