I use the same technique but like a bit coarser prep, usually 800 grit wet/dry but have used as coarse as 600. The canopy of the Buccaneer that I posted elsewhere was aggressively scuffed with 800, yet after a few coats of clear you would never know. Caution: when buffing out, you can cut through the paint very easily and it is hard to repair (ask me how I know!). 

If it hasn't been mounted, it can be painted from the inside. If this is the case, let me know and I'll post further.

Olympic finished? Pics please. I had to take a break from mine but it is back on the paintstand as I type. Lets see, Clear vs Primer...I've only done clear over the scuffed plastic. Last painted canopy I did was painted from the inside w/R/C car plastic body paints. The one before that was carved out of balsa. Going out on a limb here but I'd say that putting clear on first like Ty suggested is a good idea. In my experience, clear has better adhrerance than primer. After that, I would think that finishing up in primer, paint, clear again etc. would work fine. Personally, I would stay away from the non-dope type fillers/primers. I know many use them but they take a relatively long time to set-up and I have found that they often soften when used as a base for butyrate dope.