I've always used either Randolph or Cooper when it was easily gotten, Sig is my next choice! You can usually find the first two at the local airport and I've always been able to purchase it at a more reasonable price than the model suppliers.
Nitrate fills the grain more quickly due to more solids in it, but it ain't fuel proof at all, so you must then apply butyrate over it. Don't try to apply nitrate over butyrate, it will attack, and it will win!
I like to apply silkspan or carbon veil over the solid areas and of course, the silkspan over open bays. I stop applying the clear a little before the ship starts to "shine" from it. That is usually a couple of coats early but the blocking coat usually finishes it off enough that the final color shows no grain or otherwise. I do most of my sanding (ugh) on the blocking coat, I use platinum grey for that, and then repair the areas where I sand through to the clear.
This is by no means a complete finishing lesson, but it sounds like you needed a place to start so this is quite brief but will supply that starting spot.
Blessings,
Will