In the opinion of you guys would I be better off tracking down a copy of or ordering 5 online for PS3 since I don't have a 360, or a copy of 4 or 4 Evolution for the PS2, in terms of learning the game system and characters?
Imo, get 4EVO, and go through the tutorial... Not too much to learn in 5, except Offensive Moves (up or down + PKG), 0-frame throws (which were in VF3), and throw clashing. All of those have been removed in FS from what I remember. The only thing you have to worry about learning is the bounce combos, which were tweaked in VF5R, and eventually balanced out in FS.
I will say though, some characters got beef the hell up, like Brad and Goh, but most of those buffs were from VF4:Final Tuned, which no one outside Japan saw.
Just don't practice the combos too much, since alot of them changed. Some are still possible though, but with 5 there were better options to combo with.
If you do end up getting VF5 for the 360, you can always level up online. VFDC has a steady matchmaking/ggs thread, and I can get matches in with you, since the netcode is actually the most stable for a 3d fighter (DOA comes in 2nd).
Which character(s) are you trying to learn???