I've used a similar product (Martha Stewart Crackle Paint, no longer available, in white, brown, and red-brown). I use a hobby knife or similar tool to trowel the stuff down, maybe 1/8" thick. One thing to note with thicker laydowns, as it dries and contracts bigger cracks will appear, sometimes all the way down to your base, so prepaint it in a useful color; In my photo, the white base has a layer of blue at the bottom, to work with icy shadows.
I usually let it dry overnight. After that, you can paint and drybrush it all you want. If you apply washes, be aware that the crackle will absorb water and soften up, then harden again as it dries. My jars of material are mostly dried out, but a little water and they're back in business.
The dried material can be a little crumbly, so try not to have it overhang the base, or anywhere else where it might get broken off. It takes sealer fine, but the underlying material is still weak.