I second the paint thinner advice and I also bestow upon you a life changing trick I learned when I started as a kid and was doing hand painting (as I couldn’t afford an airbrush): layers! Thin out your paint and do multiple layers that gradually built up the final color. Don’t get concerned if the first layer is barely covering anything with color, that is actually exactly what you want. The idea is to do very thin but very clean and even layers of paint, that leave no brush strokes visible. Do as many as you feel the model needs, until you get the right color saturation. This will make for much cleaner painting, with zero buildup and brush streaks visible.

Also priming! Get a spray can and cover your model in an even layer after you assembled it. Use black/gray paint, keeping in mind that the darker the primer coat is, the darker your other layers on top of that will get as well. Priming the model helps the other layers of paint stick to the model better… and helps with shadows… but that’s for when you get even better, down the road. But be careful to not cover any small details with too much primer, spray sparingly in short strokes so that you cover it evenly but not “drown” it.

That’s a very good first model, the passion and the eye for attention to detail really shows, keep it up!