Tim's post points out the answer to how good a finish is good enough.
It is all up to you! For a Combat Kitten, it will fly best if kept as light as you can. But if you want a really good finish, then here''s a couple things to do as you go. First is to "candle" the surface. If you are not familiar with that term it basically means to hold up the model and let the light reflect off of it at an angle where you are just seeing the "surface". That will show any major imperfections at an early stage. You want to keep doing this at each stage. You will need to put on a coat of clear to seal the filler. Using primer is necessary if you are looking to get a very good finish, but then the dope/talc filler you have used is, in itself, a "primer". A "blocking coat" is a step used before the final colors are going on. It evens out the substrate, "color wise", so that less colored dope is necessary to get full coverage. What people use varies from silver to a very light gray most of the time. This will also show imperfections quickly. Candle that layer (and all layers!
) Wet sand the blocking coat flat (use sanding blocks), and candle it. If there a re imperfections apparent that you feel the need to correct, then more of your "filler" is spot applied. wet sand and spot on the blocking coat. You keep this up until the finish is where YOU want it to be. Just remember, more paint (of any kind) is more weight. When the blocking coat is where you want it, put on the colors. You can do the wet sand/candle/more paint sequence there, too. Finally, clear coat. How much is up to you again!
As i mentioned, a Combat Kitten, being small and powered by a 1/2A engine, will perform better if kept light, so a minimal finish is what I would shoot for.
Now if you are building a stunter for competition, and looking for higher appearance points, then the above sequences can go on, and on...... ending up with wet sanding and rubbing out the clear dope final coats.
But as always more paint equals more weight. I have seen more than one stunt plane over the years go from being what could have been a great performer to not so good of one simply by putting on too much dope. It's a trade off, and getting a light finish that looks really great is not easy. It takes a lot of effort and a long time.
Big Bear