good questions. i ride a tandem, but would like a 3 seater to ride the family. rarely see a 3 seater used, so prolly not gonna happen.
sounds fun and wish you the best. guess the best thing to do is start slowly and regular practice in a non car area. we self taught our selves on the tandem and repairing the thing was a bicycle mechanics education. books and internet got me through an almost total overhaul.
update us when you find your bike and how you found it.