Well your in luck matey, they've just released a brand new book just for you!

Stalin's Europe.
1500pts is indeed enough. Thats about a good evening's games worth.
Your problem is the huge variety on offer from the USSR, I guarantee you'll end up with a whole lot more for variety purposes.
Soviet Infantry is low quality but you get LOTS and its cheap game wise. I suggest you buy yourself the Udarny Strelkovy Batalon box set to start with. Soviet Infantry is the easiest to paint in the entire game and its just as well because your going to painting LOTS.
PM BIG P, he's done a great how to guide for speed painting Russian grunts.
The Infantry is a good start as you'll need some whatever type of force your doing, Tank or Infantry.
Soviet Arty is cheap and numerous and there are several boxsets for that, BM-13's are awesome.
Tanks? Well take your pick. T34s, KVs, Churchill's, Sherman's, IS tanks, half a dozen different tank destroyers, all of which are quite capable.