Just to give you an idea here, when I shoot swimbaits (3 sizes) I will typically shoot 102 cavities. Drop shot baits - 84 cavities for one and 80 cavities for the other, 5" stick baits - 64 cavities, fluke style minnow bait - 60 cavities.
I find that its more than just more molds/cavities though. All I do is try to manage heat. There is usually a point where more mold/cavities actually will slow you down. I try to have as many molds as it takes to allow me to keep shooting in a cycle, e.g. if I have 12 molds I will clamp them in 3 groups of 4. Shoot a group and move it to cool, grab another, shoot it and move it to cool, grab the last and shoot it, move it to cool. Grab the first, pull the baits, re-clamp and shoot again etc.