Well Kevin I will share my knowledge from the pen turning world because Epoxy resins have become popular there and I have used them with good success. First off there are many types of epoxy resins out there from casting resins to bar top resins and everything in between. The casting resin is the one you want. It is durable when cured and as I said used in the pen making hobby so it has to be. What makes this stuff a good fit is it dries super clear, does not require a pressure pot to get rid of bubbles, polishes to a high shine, and as I said durable but also sticks to everything just about. That is why it gets used for pens. I shown this pen, my scrollsaw blade pen, here before but I made this last year for a contest and it was cast in epoxy resin. The 2 leaders in the market are Liquid Diamonds which this is and Royal Palm. Both are very good and not sure on price but bet they are comparable. There are many new players and I have no knowledge of how good they are. If you are just coating things you could get away with bar top resins but you want one that is super clear. Most have a yellow tint.
No to the buying gallons unless you are going to be doing a ton of these. Shelf life is about one year if stored in cool but not below freezing temps and not high heat. It is a 2 to 1 ratio mix that is crucial. We use a scale to measure the parts. Those are cheap. This stuff is water thin and thus gets in all the nooks and crannies but needs a mold to hold in place. Silicon molds are great because when sprayed with a mold release agent the resin does not stick to it. I use Stoner mold release. A little goes a long way. This stuff does not generate alot of heat as it cures because it cures very slowly. Usually 24 hours. This gives those tiny bubbles a chance to rise to the top and burst. A small hair dryer can help this too when passed over it. You do not go crazy when stirring but need to stir thoroughly getting all corners of the cup or container. That 2 to 1 ratio is critical. It will generate bubbles but will dissipate. It can be tinted and things added to it.
Without seeing the item I can not suggest what or how to cast. It can be sanded planed cut but then needs to be polished. In the pen turning world we polish with Micro mesh pads and use water as the carrier. You could put on a buffer and use white diamond and then top with an automotive wax. Good luck.