If you want to clear coat the decals put the decals on next and clear coat them (you may need to give the next coat of clear coat a light going over with polishing cloths to get rid of orange peel). Use the novus and wax but keep away from areas you'll be spraying different colours. Putting the wax on before masking should reduce the chance of the masking tape pulling the paint off. Mask the model around where you want to spray the headlights etc. and then use paper towel to cover the rest of the model (saves tape and is quicker).