Zim, there are alot of choices out there and many different ways to tackle this machine. If you are not going the cnc route then concider making the machine so that it can be converted easily. I started out actually making a cnc machine that used a taper bar. That was ok because I could contol the feeds and speeds with a simple change in the program. My limitations came when I wanted to change the taper. Also it is easy to forget to change from a straight taper to a shaft taper. When you make this mistake you will know what I mean. So in short build the machine with at least the idea that you may convert it. Use better rails and anti-backlash lead or ball scres. Stay away from all-thread as a screw. And most of all have fun.
Jim.
Something like this... http://www.nookindustries.com/acme/AcmeInchAvailability.cfm