1. too many options to list. look around the site.. there are 'off the shelf' solutions you can buy, but they're expensive.
2. same, lots of options. most go with a plywood subfloor and then vinyl or carpet on top
3. i think the best 'affordable' bumpers are Move.. you buy a kit from them and weld them yourself: https://www.movebumpers.com/
5. Again, many options.. you can buy anything from some ATV ramps fro Harbor Freight up to an Aluminess full rack.. so say $300-2000.
6. Depends where you're going. I use mine, but never plan on it. You can get a good 12,000lb at Harbor Freight when they go on sale for $299 a couple times a year.
7. Not sure what 4x4 conversion you have, but call Agile Off Road in Santee. They have the best custom valved Fox shocks for our vans.