System questions for Asterisk

I am getting ready to install a small asterisk system for my home as well as a test server so I can consider installing it at one of the offices. I have a few questions. On both possible configurations, I will have only voip lines, there will not be any standard telco connections.

How good of a cpu/ram do I need? Can I do this with lower end versions, or should I just spend and get top end?

Hard drive space. I know voicemail recording isn’t an exact science, but how much space would 60 minutes of voicemail take? How much space for auto attendent/music on hold/etc?

Thanks for any help,

Scott … mensioning