If it was simply polished, especially with hobby polish, there won't be any wax in it. What kind of polish did you use?
If you wish to keep the black, just wash the body in warm soapy water, scuff the white with 1000 or 1500 grit and wash again, then carry on as if you were spraying over primer. Mask off and re-paint the white. Clear coat is a personal choice. If your plan is to polish right on the paint, just lay more paint down to allow for some to be polished away. I very rarely use clear coat, and plan my paint work accordingly. I lay down extra paint, knowing I'll be removing some. I ensure that raised edges and curves have extra paint on them, as it it easy to burn through the high spots when polishing.