Im impressed, at 15 I had just bought my mini mill and learned how to machine, it sounds like your a little ahead?
It also sounds like you have some funding for this? How big are you looking to make this machine?
Have you considered getting a mill/drill and converting that instead. It may make life a little easier, You will also be able to use those stepper motors.
Are you actually thinking about building a 5 axis machine? If so, there are ways you could actually convert a mill/drill into a 5 axis machine. A squair column mill would be needed and access to lots of equiptment Im sure.
you may want to take a look at this site, the design for 5 axis mill that Im thinking of is how he does his mill. rotary table and rotary B axis head.
http://www.rainnea.com/cnc_5axisMill.htm
Jon