Not sure about fixing the doors, it is steel so it may be more. And as for money to keep it running it shouldn't be more than $1,000 a year. As for the engine it's better to just put either a crate 327 or 350 v8 or a 911 flat 6 in it. The interior is pretty basic so you can do anything you want with it, and there isn't always a boot on the stick. But you can definitly turn one of those into a " 'stang killer".... not too hard, if you actually do some real work you'll compete with vette's. but definitly go for and have fun.