Yeah, start small, work up. Makes sense.
The A500 should be most compatible, but some stuff will only run on A1200, of course. Not very well on some titles, I've been told Civilization is hugely slow without lots of fast RAM on that Amiga (boo! hiss! Love that game).
A little 4MB PCMCIA would do you well, the snag is, lot of them don't work in Amigas as fast RAM. A600s and A1200s, that is. Some of them PCMCIA expansions spring into life with an accelerated Amiga, or even just one with fast RAM somehow, but they're you go - you haven't got an accelerated Amiga or some fast RAM in to begin with (A1200 you can do that thru trapdoor, A600 you cannot, although ACA600 Vampire is the oddity here I've been told).