My 2 cents are that Pack Chrysalis is really good for people who have returned to the Amiga after a long time absence. There are a whole lot of useful things there that you don't know that you want. And HDD space certainly isn't a problem. What I always do after a clean install is to install this pack and remove the stuff I don't want. Since I want most of the things anyway it saves time doing it this end (uninstalling rather than installing from scratch).

Grunch is a given must as well.

I have a G5 2,7 GHz (liquid cooled) and though it got it's bugs and the cooling system tend to leak I am very very satisfied with this system. It's the one I use everyday.

A Mac Mini is the perfect beginners system since you don't have to buy anything else and you don't have to check for compatibility (or hardware) issues. With MOS it simply works. But if you want some more power and got a little deeper pockets I think a G5 Powermac (with at least a Raceon 9600 128 meg) is a more justified system (Unless physical space is a problem of course. My G5 is huge and weighs 20 kilos). I bought a Mac Mini 1,25 GHz first, and though it was a nice first use I never turn it on any more. Though I should have waited for a 1,5 GHz with 64 meg VRAM like everyone already mentioned.