Depends on how old you are and how long you want to take doing this.
I'm only going to talk Mk2. Dont really care if the Mk3 rusts into oblivion to be honest.
If you're going to do this outside, find a decent car to start with and get a cover. Mk2s are beginning to leak around the heater in the cabin, hence floorpans rusting. A cover and straps will protect the majority of the water hitting the interior. And if you get water in the car and its left to stand - mould will be on its way pretty quickly.
Then you can do whatever you want at your leisure.
If you can find a local lock up garage you can rent somewhere, then that is even better. But you'll still need a cover.
Whilst your working on it just get a Stat off road notice on the car. DVLA will leave you alone then.
Regards,
Tin