DrGonzo- You'll find that the ss paint (assuming it's not white) will cut pretty easily. I wouldn't use a cutting pad, but rather a polishing pad with a more aggressive product (and even that's only if you need it). I've had good results with the 3M FCRC on ss, it almost finishes out well enough to wax if you work it right.
I'd use that and then something a little harsher than the #9, probably #80. After the #80 you'd probably be ready to wax but you could try some #7 or #81 and see if it contributes anything.
I'd use the NXT as it's most likely to be compatible with the oil-heavy Meguiar's products, which, BTW, work just *GREAT* on single stage. If time permits top the NXT with #26, man would that look good!
Louvers on the trunklid, I don't think so

Do you mean black louvers covering the rear window or something else?
I haven't done a vinyl top in, gee, twenty-some years and the stuff I used then isn't around any more. The trick is to use stuff that won't just run off onto the paint if/when it gets rained on, so at least buff buff buff to get any excess off.
Oh man does this sound like a neat project, you're lucky to be working on it.