I agree with everything fenrus said but I would add a few things.
- I went to Walmart and bought a small electronic scale. You can put your cup on the scale and zero.
- You can buy the popsicle sticks at several stores and get both large and small ones.
- Coat your work piece with a sealer like dewaxed shellac first and let dry because epoxy can seep into the grain of the wood surface, remember wood fiber is like a straw and they need to be sealed before pouring exoxy or any colored filler.
- As fenrus said overfill your cutout because the epoxy shrinks when drying. You must sand off the excess so make sure your pocket is deep enough so you do not sand away shallow details. I usually start with 60 grit to get the majority of excess epoxy off. Just be careful with 60 grit that you do not over do the sanding. Then I go to 100, 120 180 and finish with 220. Your epoxy will look dull but when you apply a top coat it will shine back up and match the surface of the wood.
- Epoxy is a great way to fill in but I have been using Easy Liner Shelf Adhesive shelf liner or Oramask 813 to mask my projects and using acrylic paint with a brush or airbrush. On some projects this works well but if you want a smooth surface then the epoxy is best.
- You can dye the epoxy with Transtint liquid. I would stay away from the powder dye because as fenrus said you must stir and stir but the powder can fail to mix completely. If you do not mix up enough epoxy and need more keep track of how many drops of dye you put in to match your previous batch. It is better to mix up too much epoxy rather than try to match with a new batch but sometimes you just dont have enough and need a second batch. This is where the scale comes in handy for mixing a small batch. Read the epoxy label for some acetone will clean up any spillage on your bench before it dries but always put paper down to keep spills to a minimum and clean up easy. You can put your popsicle stick on the paper and it helps judge when your epoxy is dried. Be patient and do not sand the epoxy until it is cured completely.