Good luck - it's a fun process!

I built something roughly similar a year or two back - here. Probably more useful if you look at the "what I would do different next time" comments!

Joe's CNC guys go rack and pinion because it is a heavily US-based community. R&P can be bought from US manufacturers who don't seem to make ballscrews which generally come from China. Not a popular choice for US builders, unlike UK/Europe. Seems to be almost a fashion thing rather than technical choice. Both can work but unless you really need R&P, ballscrews are much easier.