How many stages to start out with?

[J15BIG]

How many stages should I initially purchase to get me started on this project? I will probably mainly work on it weekends and maybe a little bit during the week(figure about 8-10 hours a week) and I tend to work slow. According to this site(www.ultimasports.co.uk/usa/prices.html), the first stage is just the frame and the floor boards. I think that stages 1, 2, and 3 should keep my busy for about a month? What do you guys think?