Ask your paint supplier as well. evercoat has a flexible filler poly-flex or something for plastics though i've never used it.
When i redid my 130 motor and cowling, alot of minor scratches you can sand out as the plastic is so thick, though I tried not to sand through the original
adhesion promotor but i did in a few large areas due to clear coat failing...no problems so far. I primed with house of colors kd2000 but they have an epoxy one as well. kd2000 is more of a epoxy acrylic. If you don't reduce it, it's a surfacer, reduce it and you can use it as a sealer. works really nice as a surfacer, shoot then sand (air DA will really make it baby bottom smooth), i pretty much use that on everything now. Low voc, no isos
For the decals, i'll vouch for these guys!
http://www.outboarddecals.com
quality is excellent! I'll be using them again on another boat i'm planning to clean up. No better aftermarket ones imho, awesome! The decal material is really top notch feeling. When you apply the decals, i used the same technique as clearbra's are installed, distilled water + couple drops of soap for slipping solution, and a 2nd bottle with some dist water+ isopropyl alcoho for tackingl. The isoprop allows you to tack spots down. So if an edge isn't laying flat, hit it with the alcohol solution and it will stick and the soap solution let's you slide it around until positioned. Like this:
http://www.autopaintguard.com/install.asp
Then squeegee (hard or soft), the decals are so tough i just used a hard squeege from the auto store (for tint) and a credit card, they don't really scratch. Have a microfiber towel for drying. Squeegee the water from inside to out. Don't worry about a couple of *small* like pinhead bubbles here and there, there will be many, though try not to have huge ones (like couple of eraser size ones, keep working those. Once the sun hits it, the small ones , water will evaporate out from under the graphic and they go away.
If i was to do it again and if the motor was newer and worth more, i'd probably take it to a painter with a paint booth, just get a better finish though mine came out pretty damn good, i just used a single stage but you could base, apply decal, then clear.