You're gonna want a white base coat under that or white primer imo. You don't want any grey scale glowing up from under it. You want a clean pink I assume.
The X series paints can be thinned with their X-20a thinner or lacquer thinner. Lacquer thinner produces a slightly harder surface, either lets the full gloss through. Tamiya gloss acrylics are just that, glossy but the wrong thinner can produce a haze in them. I've also had pretty good luck with straight 91% isopropyl from the drug store. Start out thinning it a little less than 50/50 and see how that sprays for you. With a siphon brush I shoot these paints at 23 lb fwiw. Shoot a test on something solid ( I use prescription bottles). Anyway if it goes on and doesn't level well just thin a bit more, generally you don't need more than 50/50, a couple of color I've gone a bit over on the thinner. 60/40 paint to thinner can be good or 50/50, depends on the pigments, temp etc.
Edit: on your last coat slow down your passes, make it a good wet coat. This will improve flowout and increase gloss. Again you might want to have a test subject to experiment on before shooting your model where yiou aren't used to gloss or this paint ( if I read your op right)..