Hi
I'm by no means an expert, (!) & regard my self as an 'improver', & first bought an airbrush to try & get a decent yellow finish on a Hotspur glider.
some 30(ahem) years later, I'm still trying.....
A few thoughts.... I always prime, as I prefer acrylics, to get your target as smooth as possible.
Mr surfacer 500, 1000, or 1200 can be sprayed, the lower the number, the more body & thicker the paint, for sanding. eg., I Hand-brush Mr Surfacer 500 to stipple texture on armo(u)r!
The higher the number, the finer the finish.
Thin with Lacquer?/Cellulose (test first, American isn't always the same as English )
I use Vallejo Polyeurethane primer, available in grey, black & white, gives a smooth finish,but can give a 'crumbled' effect on edges if you sand through, easily fixed with anotther touch of Vallejo primer.
Once you are happy with the Vallejo primer coat, pref. white in this case, then spray yellow over it, thin coats, several times is better than trying to get a solid coat, as acrylics are not as opaque as some.
Perhaps you have a target you could practice on?