Just my opinion, forget the aftermarket stuff and concentrate on clean building. Too many models have tons of aftermarket bits and pieces and still don't look good because the basics were neglected. You're off to a great start, keep them coming!
I've used Testors Gloss Gull Gray in the past, seems pretty close. One reason I've heard for light colored interiors is they stay a little cooler and it's easier to see fluid leaks.
I saved my nickels and dimes until I had $2.06 (sales tax) and went and bought an AMT kit. Drove my father crazy that I couldn't save more than $2 at a time