You wont need a whole pot of tamiya for 1 coat of a 1/6th scale kit, depending on the cup size of your air brush will alter my next statement...... I have an Iwata HP-C? i think thats right... anyway 1 full cup of thinned paint will normally easyly cover a 1/6 kit, it goes a lot further then you think! but saying that it also depends on the colour your spraying... some colours cover better then others, blues and greens for example cover very well and may only need 2 coats (2 cups of paint) to get perfect coverage, colours like red and yellow are crappy for coverage and will normally require a white base coat then several very light coats of the colour (3 or 4 cups of paint), bare in mind that the more coats you have to apply the thicker the paint build up so always do multiple light coats rather then thinking one heavy coat is better!
I cant stress enough how important experimenting is, depending on paint,airbrush,thinner, compressor, climate, primer ect may completely change how you mix and apply the paint..... keep experimenting untill you find what works for you mate, yes you may waste some paint doing it, but once you are happy with the process you will make less screw ups down the line!
Oh and the cardinal rule of using an airbrush! ALWAYS clean your brush between each colour, and when you finish a session break the brush down and give it a good once over and lubricate the moving parts, your airbrush is your best friend so keep it clean
I learnt this the hard way, now no matter how boring it is I religeously keep my brushes in top condition!
