Bill,
Look at this web site for some cool P51 paint schemes:
http://www.mustangsmustangs.com/p-51/p51pastpaint/home.php As far as paint go, since you have fiberglass you may want to apply the covering with nitrate as it seems to adhere better. I would do two thinned (60/40) coats of thinner/nitrate on the silkspan. Let that dry a week ish, then switch to Butyrate clear SIG Super Coat (this is a taunting dope). Give it four - five coats of 50/50 clear super coat to fill the weave. Let it dry a day between coats and at least three days after the last coat of clear. Candle the surface looking for dry spots or rough spots and repair. On the solid surfaces you can apply the dope/zinc stearate filler. Once dry sand most of this off to get a smooth surface. Once all is smooth, if you are going to use a light color top coat, spray on a coat of cream color butyrate. This is the first fill/base coat, let it dry at least a day, carefully sand off most of it to get the surface smooth. Spray on a second coat of cream, lightly sand and candle. Fix any dry spots, fuzz or low spots.
If all is smooth, tack rage down the surface and spray on a coat of clear Sig Lite Coat, let dry a day or so. Lightly sand and start appling the color finish. Once finished, let dry about a week and check that the edges of the trim tape lines are smooth (you can use old credit cards to shave the edges down smooth). Start the clear top coats, I use 40/60 Sig lite coat to thinner. I start around the frame and cap strips putting on three coats, then start doing the whole ship. Do one coat a day, I use five coats if using just clear dope.
If you are going to use "Death Paint" top coat you can do the frame with two coats and then two coats over the whole ship, let it dry a week, then spray on one lite coat of DP let it cure out then I do a second coat on the fuse and top surfaces. Let it cure out a week and its ready to polish or fly.
Good luck with the finish, let us know how it comes out.
Best, DennisT