I thought I decided on a TT, Now studying Class C

The Ford V10 is a good motor overall. Early ones had some trouble with spark plugs being ejected if not carefully torqued down during installation due to a bit of poor design of the head (only a few threads holding the plug in), but that was resolved after a couple of years. With proper care and maintenance, the Ford drivetrain is pretty much bulletproof and likely to outlast the house part of the motorhome.

IMHO condition is more important than either age or milage, though of course all are related to a degree. Do check very carefully for leakage in the cabover section of a class C; this is a very common weakness, and the ensuing damage can be quite costly and/or time-consuming to repair.

With the right floor plan you go as short as you want. 30' and above starts to limit your campground choices. We have a 28' with plenty of room and storage as well as a 30 amp system. We have no problems finding a cg. Some state park cgs have very short sites but beautiful views. Ours fits those sites (without an extra vehicle in tow).

When you locate one of interest have a trusted mechanic do a thorough check of the engine, transmission, wheel bearings, etc. That check up can save you from spending thousands on a lemon.

I started by looking at TT's and then went to van campers. Finally felt we had found the right "feel" with a short class C. We didn't have a tow vehicle so that entered into our decision. We have been super happy with what we ended up with. I felt the TT's were pretty expensive for just the house and not the truck part. Truck plus TT would have cost more than our C.
32' might be the limit on size in your price range. The larger Class C's are on bigger frames called Super C's and pretty pricey.

stevec22 - Decide what type of camping you will likely be doing. We are the type that rarely stay in 1 place more than 1 or possibly 2 days. We travel to visit friends or see nature. For us, a motorhome fits us perfectly.

The other type will drive 1 or 2 days and park somewhere for a week. A travel trailer might be better suited. You will have more elbow room for the money.