There's lots of people full timing in TTs. Maybe more in 5th wheels and Class As, but still a lot of people in TTs. And surprisingly, some of them in fairly small TTs.
Starting out in a TT, and a used one at that, is a good way to see if you like full timing. If you want to move up to something larger, you can without taking a large financial hit on the TT. Another reason to buy used is even if you want to stay with a TT, you might want to change from your first one for either a larger one or a different floor plan.
Bill