Applying the stencil the day before should not have been an issue since you said it was kept warm. I agree with Pablito350 in that it looks like it was applied too thick and may have been too thin. Unfortunately, there aren't a lot of options. I've found, that if you have a deft hand with an airbrush you can blend out the runs and get a more authentic look than with a paintbrush. It ain't gonna be a fun time regardless.

Yes, more light coats is always better than fewer heavy coats. That goes for pretty much everything. The struggle for impatient people (me!) is waiting the proper length of time between coats. Latex isn't a big deal but some finishes have long dry times between coats. This is especially true in instances where you are applying a different composition coats (e.g. oil vs water)