Welcome to the forum.
Unfortunately there are no quick easy answers to your questions. This forum is also searchable. Many of us do a lot of reading.
This CG site has a lot of info. regarding much of your possible research.
RV Checklists
The whole Gas VS Diesel algorithm is another topic you'll need to weigh as no two persons have the same requirements or budgets.
You might wish to enlist or even employ the help of a RV surveyor that is experienced in the particular style, make, and models you hone in on. Seemingly expensive fees can pay for themselves VS costly hidden system repairs etc.
Buyer Beware are your marching orders in the this hobby, past time.
Best of luck.
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J & J, DRV Suites ES-38RSSA #9679
GM Denali, 3500HD-Max, 4x CC, 8' DRW,
EZGo-TXT, Clubcar Precedent