I agree that the newly updated iMac would suit your needs quite nicely. The Mini might not be enough, and a Mac Pro might be too much for your needs.
Leopard will run you about $130 if you buy a machine now. Is it worth it to wait another ~3 months to save $130? Only you can make that call, I suppose.
Lastly, congratulations on your decision to switch. You won't regret it!!