Advice - Mk3s were the best shells, minis were in there prime then so blmc chucked money at them left right and center, there a better grade of materials and generally had more care and time spent on them in production. Buy one with a v5 full stop, don't buy a ID'less shell just on the merits its solid. If you are buying a project, make sure you know all the work that's been done, buying a shell from a mini 'expert' to find on its first mot it fails on substandard welding isn't cool. Also find out what's there and what's not there, check over what's been removed from the car and look at the condition, generally set yourself up to walk away from a few, minis take very good pictures(just look at prawns ). I'd also advise if your buying a project shell, buy something unpainted if it's been paneled. You know what's under the paint then, rather then finding a skin of filler falls off the rear quater one day.
Spend asmany hours as you can searching through project pages and build diaries. You'll find out more what to look fors reading those then you will speaking to folk.
Just enjoy it too, and when it's built and finished, don't expect it to drive like a fiesta or a micra. It's a much much different beast.