Any reason why you're adverst to using an airbursh? Its probably the right tool for the right job. You can find them pretty cheap - even a junky pache airbrush for Tshirt painting would work ok. I find that the thinner I can paint - the more fliexible the acrylic is and the less its opt to pull away or develop cracks.
You can also work to prep/clean your surfaces more to make sure that the acryic will bond to it better.
There are mediums out there (they go by differnt names) that you can mix to increase the flexibility and bonding properties of your acrylic as well. Seach the moster makers website and some sites for Tshirt / leather jacket painting - they'll have good paints and good additives you can use for better success. I've airbushed a lot of leather jackets and a lot of latex appliances and have experimented with many techniques, and additives really do make a difference.
Low quality Acryiic (yeah it does vary in quality) applied too heavily/thick will get less flexible and crack more than a thin layer of acrylic applied with an airbrush to a good clean surface.
also to seal it you want to use permawet or a meduim gloss from Michaels, seals it off and prevents from cracking.
also airbrush is the way to go man as cathat said for many reasons.dont use up alot of money on a nice mask but go cheap on painting
it . youll regret it in the long run bro. best to do things right the first time for sure !
if you really really really dont want to use airbrush then (even thought i wouldn't anymore) go with a acrylic pen from micheals for the
spots, get black and shape in the dots etc. but you cant really get those nice tones you get with a airbrush.brushes only get so far and they
are a pain, they cant get that perfect tone, build up paint and make a mess.