The things you describe sound minor. You should expect to buy a new battery (3 years is a pretty good run) and new tires within a year.
A lot of folks get excited about the appearance of the roof. I guess I am too short and I can't see it. I don't really care what it looks like as long as it doesn't leak. You should get a firm commitment from the seller that it doesn't leak. But I don't know that there was a better way to repair it. Just to make sure that the epoxy doesn't pull away from the aluminum skin, I might have suggested a well-caulked aluminum patch over the epoxy, riveted into the existing roof. But that is small stuff.
The 8-10 inch missing piece on the side sounds like a pocket stop cover. These are shown in two pictures in my Tech Album at
http://www.trailmanorowners.com/foru...pictureid=1280 and
http://www.trailmanorowners.com/foru...pictureid=1279. If so, these are appearance items. You can buy new ones from the TM Parts Catalog, or leave it off. I am under the impression that TM is not installing them on new trailers any more.
Peeled and chipped veneer inside is an unfortunate fact of life for some of us. It happens for various reasons, but is certainly no more than an appearance item. You need to judge what that is worth to you.
NADAGuides says you might expect to pay $17,600 average retail for a unit with air conditioner and awning. The price will vary a bit depending on other installed options (though none change it much) and location (west coast is a small bit pricier than east). NADAGudies is by no means holy writ, but it sounds like the seller is in the right ball park.
Bill