OK, this is an interesting proposition!!! My gut reaction is you should jump on it. Random thoughts:
*219k is a lot of mileage so you can assume it will need some suspension work to improve the ride quality. But suspension work is EASY and not very expensive. You could do a really good suspension kit and improve the ride quality a lot.
* Brakes are easy peasy lemon squeezy.
* Interior TLC goes a long way. Carpet is easy to replace and seats are easy to re-cover. If the carpet is rotten, just yank it out for now and spray down some LineX.
* You'll need an engine rebuild (eventually). These engines are not hard to R&R, just take your time and photograph and label everything. Determine your budget and make a plan. Some of us love spending other people's money, so a 306 stroker, forged rotating assembly and ProCharger make a lot of sense to me personally. LOL.
* Last but not least, in terms of idling rough and stalling from a stop, the very first thing I would look at is to see if you have plugged cats. Not to be crass, but that symptom of "constipation" is because the car might not be able to pass exhaust gas. Pun intended.
NOTHING BEATS A PROJECT MUSTANG WITH YOUR EYES WIDE OPEN. EVEN BETTER THAN THAT IS HAVING YOUR DAD AROUND TO HELP.
Go for it. No brainer.
Andy