It's a good thought Neil,
I'm sure there's plenty of us here would like to do the same.
But if you're looking at tackling the big stuff you need a very large well equipped workshop, with a lot of expensive tools. That's going to be a large overhead and your work rates are going to have to cover it. Initially you'll be paying for an empty workshop some of the time until you get established.
May be easier to specialise in the smaller stuff, Land Rover, Jeeps, Champs at first.
Good luck whatever you decide to do.