Use only natural hair 'chip brushes' with resin.... you can get them for about $10 a case at Harbor Freight.
Do not throw chunks of curing resin into a trashcan with other refuse... they get VERY hot when they react, you could start a fire.
If you use the white plastic top that came on the resin tub to mix in, the resin does not bond to it.... when you want to mix up your next batch, flex the container and break out the cured resin, and use it to mix again... over and over.
When one batch 'kicks'... or cures and becomes hot, it will speed up the curing time on sucessive coats..... use this to your advantage to build up thicker areas when desired.
Resin shrinks a bit on curing. The hotter the cure ( the more hardener you add) the more it will shrink. Stay as close to the suggested ratio to minimize shrinkage.
Buy extra tubes of hardener when you purchase your resin, it's always good to have on hand if you run out during your project.