If you're only going to do OCS/ECS stuff then to be honest there probably isn't a great deal of difference. But in your case I wouldn't really bother too much with the latest AmiBlitz versions; 2.1 will certainly do more than enough for you.
There are some tutorials for Blitz on the
Amiga Magazine Rack which may interest you; try Amiga Format issues 52 and 60-66 for quite a lot of stuff. Also Aminet has loads of source code for various different programs; I also have quite a lot of examples etc myself on my Amiga at home if you would like me to upload them for you at some point.
There are probably plenty of sites with Blitz-related things on them I'd imagine but none spring to mind right this minute
