1. The VIN on my 1993 F53 Newmar is on the driver's doorframe. There is only one VIN on mine, the one I used to register and license it. Which I have ignored ever since. For my chassis and drivetrain parts lookups I've only ever needed to know "1993 F53". Try it at RockAuto, Advance, Autozone, any of those online parts places. They don't care about your VIN.
2. Perhaps someone more familiar with vintage Bounders will know.
3. The fuel filter is a metal "can" on the inside of the driver's side about four feet back from the engine.
4. The schrader valve on the fuel rail is old school standard and doesn't have a size designation that I know of. Most fuel pressure tester kits come with a fair selection of fittings. I know the cheap one I got from Harbor Freight did. As sis the better one I bought from Mac Tools. I've never seen one for "Ford Only". What kind did you buy?
5. My somewhat different F53 doesn't have a relay cover like that. If it were me I would remove the obvious screws holding the cover on so I could flip it over and actually see what is holding the relays on.
I take it you are having fuel pump issues? There are a couple of good threads about getting fuel pumps sorted out in the Ford chassis section. One of which I started if you want to look. https://www.irv2.com/forums/f23/rela...es-508562.html
If your coach has been sitting a LONG time without being started, it's pretty common for the fuel pump to "stick" and not run. Gasoline gets old and gummy. In mild cases sometimes you can tap the pump and have it break loose and run. I personally wouldn't consider a pump that had stuck to be reliable, even if it does seem to work. In cases where the gas is pretty bad and the pump is actually visibly gummy, you just have to replace it.