As to the frame, I'd go ahead and clean it up and paint it as long as You're this far into it - I used a silver POR-15 on this G14 frame and it went on pretty easy, seals and prevents rust, and has already proven to be quite durable (I had a good sized piece of 3/4" pipe accidentally fall on the frame - long story - and it didn't leave a mark) ...
20161118_141017.jpg
As to the body, the most important part is to make *sure* you have everything clean, clean, clean - then apply a good adhesion promoter prior to priming and painting. Dupli-Color makes a spray-bomb adhesion promoter than I have used in a pinch and seems to work well, but I'm sure others will have products that have worked for them too. There's a great thread on painting carts in the "Body and Paint" section, here's a link to it:
http://www.buggiesgonewild.com/body-...ic-bodies.html
As to wheels and tires, make sure You go with at least a 1" offset, with a 7" wide rim that would mean either 3:4 or 2:5, also with the LT kit You have to go at least a 10" rim (I prefer 12 minimum or even 14's - the pic above is 23X10.5-14 tires on 14X7 rims with 3:4 offset) - also make sure the tire is a minimum 4-ply (preferably 6ply) as a lot of the cheaper 2-ply tires will give You excessive tire-roll and are sloopy to driveon at speed.