If you are flying with electric power you don't need any topcoat but to be honest I haven't found the perfect top clear coat that I like but here is the process that I used on several models.
1) Build as normal and then fiberglass the airplane with one ounce fiberglass cloth, using the Z-poxy finishing resin. for open framework I use Solartex covering which is iron on and is ready for primer and paint, but they do offer colored versions. there are lots of sources for fiberglass cloth
http://shop.balsausa.com/product_p/564.htmhttp://cstsales.com/e_glass_cloth.html?gclid=EAIaIQobChMIkIWK7b371wIVmLrACh3eLwSHEAMYASAAEgJP-PD_BwEhttps://www.towerhobbies.com/cgi-bin/wti0001p?&I=LXCX58&P=72) The primer I have been using is the rattle can primer from Ace or Home Depot, most of it gets sanded away. White for light colors and the grey for darker colors. The color of the primer affects the final color of the model. Try a test panel first before painting the real model
3) I get a good quality exterior grade latex house paint and get it mixed to my color chips at the professional paint store or Home Depot. I typically get flat paint and then apply gloss clear later. I also use a large air paint gun with a large compressor. I will thin the paint with windshield washer fluid, you have to try different ratios but the normal paint is too thick for the air gun. The windshield washer stuff sounds odd but lubricates the gun and doesn't change the color. I don't add much to thin the paint, if too thin it might run and if too thick it can splatter in large drops. Try it on glass test panel to check the air gun pressure and paint mix. I always do test panels before the real model.
4) apply ink lines
5) Apply decals
6) clear coat - still looking for the one I like best
Fred