Thanks!
First thing is first... Start with a Jetfire so you can take advantage of the short nose.
I usually prep every single part by sanding it thoroughly, ESPECIALLY anywhere that parts touch or rub. If you don't prep these areas by adding some clearance for the paint that will be applied you'll wind up with lots of transformation scars.
I took the nose blisters and cut them off with a razor, then moved them down, filled the seams, and sanded them. This is a tough thing to do because of the lines where the nose halves come together. Thorough sanding will again save you a lot of misery.
I'm not a firm believer in primer. I think it can help, but if you use a quality paint it is not necessary and can be a detriment to keeping paint on the toy because it will make the overall paint applied thicker.
Finding custom parts is a must unless someone has some VT-1 armor lying around.
Pine-Sol works well for stripping paint. I use that on areas I can't get the stuff off with sanding.
What else???
Once everything is done... Clear coat. Apply decals. Micro Sol the decals. Clear coat. (Dull coat if necessary.) This makes the decals appear painted on.
Decide what mods you want to use and go for it...
Best of luck and keep us posted.