Tooling and tool holders:
http://www.maritool.com/ is a good place.
We have an manual lathe and it's great for anything round, spacers, shafts, pulleys, etc. You can do a lot on the lathe that you can't/really don't want to do on a mill; even with an 4th axis.
Sounds like quite the setup you guys got. What kinda tools depends on what you guys know/like to use and what parts you want to make. I echo Mike's question, what kind of experience do you guys have with fabrication?