I started by doing what you're doing now...I ripped EVERYTHING up. I then did the wirewheeling stuff, scrubbing with TSP, primering, blah blah blah.
I laid out a grid pattern of 1x2 furring strips on 16 inch centers. They are glued down with liquid nails to prevent squeaks and are screwed down with some 20 year screws that the hardware store was really proud of ($$$).
Between the furring strips I cut 3/4 inch white rigid insulation. This is where I differed from a lot of people as they use the rigid pink stuff, but it really was an issue of price. I just got a really good deal on the white stuff, even if I lost a little R-value. I think the difference was right around R1-R1.5 between the two (I don't know the units that are attached to that
On top of the furring strip/insulation floor which was now flush since 1x2=.75x1.5, I put down the vapor barrier. I had to trip it a little, but it runs up the walls about 6 inches on all sides. I stapled it in place. I'm not sure if that was the right thing to do as my impermeable membrane is now permeable to a slight degree, but it needed to be secured somehow!
After putting in the vapor barrier we laid down sanded plywood and screwed it in place. At that point you can chose the flooring of your choice. I have some industrial carpet up front and had some nice plush stuff in the rear until a little accident involving 55 gallons of fresh water and some veggie oil. I'm thinking laminate this time....
My walls are bone stock the way they were. I just didn't want to mess with a good thing, especially given the all around great shape my floor was in. I just didn't see a need. The only thing I did was run a 2x2 across the floor all around the edge along with another one on top of the seat rail. I ran all my plumbing and wiring through those chase panels and covered them in 1/4 inch luan.
I'm not really sure what you're going to need to do with your walls. I know some people on the board dug far deeper than I did. In the end it's just a matter of what's going to be best for you. I can tell you I'm very happy with my floor. If I could do it over again I would have used slightly thicker plywood. It's not that my floor is soft...it's just that it isn't solid like steel either. It's actually kind of nice to walk on, but I occasionally worry about longevity. Again, it was simply a matter of finding a good deal. The floor did do a great job of cutting down on road noise and noise from a whirring AT545, the driveshaft, etc. It also has always seemed pleasant to walk on (no hot spots along the exhaust pipe!), but I'm not a winter camper....yet. If all else fails I can just through down some area rugs or put on a pair of slippers.