A flood coat is thin but greedy: it self-levels, runs over the edges, and a shortfall shows up as a dry stripe you can't blend in. Get the area-times-thickness math right and pour once.
Volume is surface area times coat thickness. For a rectangle that is length times width; for a round top it is pi times the radius squared. The calculator multiplies by your number of coats and pieces, then adds the edge overpour. One US gallon of mixed epoxy fills 231 cubic inches, so a gallon covers about 12 square feet at one eighth of an inch.
Raw wood, especially end grain and live edges, releases air as the resin warms. That air rises through the flood coat as bubbles. A thin seal coat brushed on and left to gel first blocks those pores, so the flood coat stays clear. Set the thickness to the seal-coat value for that first thin pass.
Not with table-top epoxy. These resins are rated for roughly an eighth of an inch per layer; going thicker traps curing heat and risks yellowing, dimpling, or cracking. If you need more depth, pour multiple coats once each has gelled, or switch to a deep-pour formula rated for the thickness.
The overpour allowance covers resin that drips off the edge during self-leveling. If you intend to fully coat the vertical sides as their own surface, add them as extra area rather than relying on the overpour percentage, which only accounts for run-off.