Yes model T have a large spare parts market. Austin 7 to my knowledge do not have the amount of spares available. Yes an Austin 7 will take 4 people but a friend of mine who owns one doesn't recommend it. Why limit yourself to two models, Chevrolet have a pretty good aftermarket parts supply and are easier to drive than a model T with a conventional floor pedal set up. Other brands of which there are many, may not be as easy to get parts for but i have found over many years you rarely need a lot of parts. I would suggest you attend a vintage section meeting one night and talk to other members with a variety of cars to get a better understanding of driving and maintaining these cars. Hope this helps.