Buying older motorhome as first purchase

That's what I'm working on now. Mine is a '98 on a ford superduty chassis. The older a unit you get, the more you don't get some features that are either standard or even options on the newer units. I would recommend you get the E450/superduty unit, most units tend to be heavy and with the E350 chassis, there's extra weight for stuff you want to take. Some options are possible but a pain to install, electric windows/doors/mirrors. First couple of years of the Triton v-10 weren't as reliable as the later years. I'm finding just replacing older fittings to be time consuming. I went to change the light bulb in the shower, and the lens cover crumbled. Just recently had to replace the toilet valve. Part wasn't expensive, but access to it was restricted. Really have to be careful with water damage, especially around the cabover. Class C units historically have issues in this area.
Rv repair/maintenance by an rv repair place is expensive. Some times you can get regular truck repair place to do some of the work. Except for a few services, the Ford dealer is about worthless.