HELP! I sprayed my BMD-1 with tamiya colour spray. I didn't use a primer, as apparently you don't need to as the spray itself primes.

I have practically zero experience painting flat colour on tanks. My steel legion armour was easy because it was dry-brushing a lighter colour over black. This time, I am not dry-brushing, merely painting a darker colour over a lighter one (camo and catachan green over khaki) but the thing is, it looks like shit. If I do a single coat the lighter khaki shows through the brush strokes. If I use more paint/ do layers it's too thick and also shit.

The catachan green doesn't even drybrush well at all...

thick and horrible

I'm requesting help on what to do. Do I just add more thin layers and build it up, or buy an air brush.
Also, in either case, to get clean lines for my camo patches I have to mask with blutack /putty right? How do my Imperial Guard comrades paint their camo (if their scheme is dark over light basecoat?)?