General respray advice

I'm thinking about getting my XJ resprayed in the next year or so, before the rust really takes hold, and since I've never attempted to prep a car before, a little advice would be much appreciated. I'd be planning on doing as much as the prep as I can myself, in order to cut down the final bill, and would be looking to get it resprayed in either the same shade or one near. I'd also probably take the opportunity to replace the hood and wings, since they're slightly dented, and would assume that the easiest way to get them to match up would be to have them sprayed off the car, but at the same time.

My Xj's a gunmetal grey colour, and I noticed that there are layers of clear lacquer on top of the paint surface. What needs to be taken off in order to prepare it for the bodyshop? What abrasives should I use? Are there any special things I should bear in mind regarding oxidised paint - I've got oxidation on the roof and would like to get that sorted properly. Also, should I think about using filler & rust inhibitor on rust patches - there are a few little bits near the gutter and behind that grille thingy to the rear of the rear windowglass? Thanks!