There is a lot more checking than I realized, and I'm afraid filling these gaps by just pouring in epoxy will be difficult. I want to keep the live edge and avoid making a complete deep pour epoxy mold. Some of these gaps go all the way through The 2-in slab. Any tips for me?
Yes. I epoxy filled some voids in a wood top for a desk I made a few years back. I used frog tape (fancy masking tape) on the bottom and it worked fairly well. Some epoxy still escaped and some of the tape was a bit difficult to get off. Be sure you do this over something like waxed paper for easier cleanup.
Like you, I tinted my epoxy black.
I used disposable cups for measuring, measured by weight on a digital scale (don't forget to weigh an empty cup), and mixed with a popsicle stick. Pour on the top around the cracks. Don't go too nuts on the first pour and let it fully cure. It will work its way into the cracks if you're using a crack filler - that stuff is very thin. Why not go big on the first pour? It will minimize the mount of leakage you get on the backside.
I sanded the top down afterwards and finished as per usual. The fill is very low key, which is what I wanted.
Pic of the desk being used. Look for the black between the boards.