Neat project! I formulate epoxy resins professionally, and I enjoy seeing new uses for my favorite polymer!
What epoxy are you using? I would suggest you have a plan in case the resin exotherms. I have personally had a 1L batch of resin with a quoted potlife of 4 hours exotherm in a half hour. The worst case scenario for exotherm is mixing a big batch of resin in an insulating container. Using a metal mixing container should help, as will adding the filler. If it does run away, there won't be much you could do to stop it-- a garden hose might be the best option.
We generally use 5mil nitrile gloves and safety glasses as the minimum personal protective equipment in our polymer lab. The amine curatives (B-side) can burn skin and eyes. The actual epoxy (A-side) tends to be more benign, however you can become sensitized to it with repeated exposure. If you get any resin on your skin by accident, wash with soap and water-- never acetone, as this allows the chemicals to penetrate your skin.
The A-side and B-side really should be weighed out on a scale prior to mixing to make sure you get the proper mix ratio. This ensures that you get the best cured properties. Also, thorough mixing is critical.
Sometimes we have filled samples that settle during cure. Essentially, the particles fall to the bottom of the sample, producing a resin rich layer on top and a filler rich layer on the bottom. Since epoxy shrinks on cure (though less than almost all other polymers), the resin rich layer contracts more than the filler rich layer, and the sample bows. You are shooting for a very high filler loading, which should prevent that, but if the resin does pool on the surface of the casting, it may be worth removing before it fully cures.
Hopefully the resin manufacturer provides a recommendation for cure time. Most ambient cure systems I have come across continue to gain strength over the first week or 2. Heated post cure improves the properties of most epoxy formulations, but you have to make sure the heat is applied slowly and evenly to prevent the possibility of warping.
I wish I could come help out with this project, but I'm on the other coast. Please let me know if I can be of help remotely.
Nic