The round body 4 door blazers have what you need. Bravada's all had "leather" and other fancy interior bits. The seats swap right over, and there is a plug taped to the floor under the carpet for the seats. I believe it was just in front of the hump for the rear seat, passenger side. If you find a bravada, you can also grab the door panels and the home link stuff. Personally I couldn't care less about homelink, but it also has more features for the overhead console like average mpgs and range. I think they also had a self dimming mirror that's on that harness too. And lighted visors. Other things I also pulled from a 99 bravada were, glove box light, roof rack (for my topper, same as the zr5 but with longer rails), dual 12v outlets under the dash on passenger side. If you can get it out, bravadas and awd Astro vans also have a 1 piece axle shaft in the front to get rid of the disconnect. The bravada seats are a big upgrade over the stock cloth seats I had. I didn't like sitting on the floor, and the heat is nice. I wouldn't worry too much about a rear seat heater, the rear seat is kinda uncomfortable to sit in if your are bigger than a 12 year old. I very rarely have people in the back seat. I did however put another 12v outlet in the removable plastic cover of the center console.
For the rear seat, the only bolt in is from another crew cab pickup. There was a guy that swapped in a blazer seat years ago, I don't remember specifics, but should be able to search here for it, pics could very possibly be dead. As for the rear door panels, again only a 4 door crew cab for a straight swap, but there was also another member here that grabbed the rear panels from I believe a 95-97 4 door blazer, made a tool to melt the plastic on the back to remove the "leather" part and put it on his door panels. I never tried it, but did find the panels, have them in the shed, it looks like it'd work fine. I don't remember what he did to attach them to the stock panels. Epoxy perhaps, I don't know.
As for rust, I would think that by line x ing it you would be sealing in whatever rust has already started. Mine is starting to get bad around the rear corner passenger rocker and front rocker under drivers door. I don't know what I want to do. I took all my flares off and the bed has some bubbling around the holes. Another spot to look for rust is the front bed mount, the sheet metal channel that the bolts go through. When I was crew cab shopping, I would grab the bed and lift it to see if it moved. If so, next truck. Disappointed some salesmen I'm sure. Same with the flares, if they were loose, next truck. The flares cost so much to replace its kinda dumb to be worried about. I forget who, but someone here took the flares off, put some "buttons" or whatever you want to call them in the holes for the flares and had it painted over, was pretty slick. I like the look of mine without flares.