when I first started back into the hobby, I handpainted as well. This was before I got an airbrush. The key for me was to thin the paint, especially if it's enamel (the little testors paint bottles). I would thin about 50/50 with thinner for an even coverage and so the paint won't clump when applying. Plus, you have to wait for each coat to dry (24 hrs) before you apply a second coat, if needed. If you don't , the second coat will eat into the first and create an unsmooth surface. However, I find acrylic paint applies and covers much more even than enamel when hand brushing. You also don't have to wait to apply the second coat ( maybe 5-10 min). If you choose to handbrush, you may want to give acrylics a shot. Just my $0.02 worth......
Andy