My Amiga 600 setup, before it died on me:
1MB internal RAM expansion
2 external floppy drives (only one works now)
2MB PCMCIA RAM card
4GB 2.5" Harddrive
Kickstart 37.299 (or was it 37.300 to run harddrive?)
Personally I found 2MB plenty for my software development, but it depends on how fancy you plan to go - I only develop for those with 68000 CPU's and no FPU/MMU, those with FPU/MMU might be able to run them too.