Stripping / Painting / Coating / Cleaning Rims

I'd strip to metal so you can match the undercoat/colour manufacturers (although is going to be a longer/more expensive process), for the best finish use loads of thin coats with as much drying time between as you can bare..?

I think you need to apply the colour within a certain period so that you form a chemical bond (and not just an mechanical bond) - let it dry too much and you will not get that chemical bond, you would have to check with each manufacturer (ie: read the can) but they often recommend leaving just 15-30 minutes between each coat so that you don't plie the layers on while still wet (which can cause runs and pooling) but so that the previous layers becomes tacky but not dry.

I agree about going to the metal if you want to do a 'professional' job, in that case I would simply Nitromors the frame and not sandpaper it, but I still think that for most home spray jobs using the base already there is better as it is likely very well bonded to the frame.