I love this mod, but too many critters for my tastes, would this cut back on the number, or would this mess something else up?
do I have to use the overspawn?
or is there a reduced spawn mod floating around out there somewhere?

peace
So, you will lose much of the content, spawns, undead, new goblins and horses among other things. No, there is no reduced spawn esp, but if you want you can make your own esp to reduce spawn rates or the numbers of creatures, depending on what you want removed.- WAC - Overspawn.esp This esp rework the vanilla creature lists, this one also add the goblins of WAC that aren't touched by the WAC.esp at all. Overspawn make a big difference and you will not see some stuff without it, for example, the new horses of WAC are managed here. This will conflict with anything else that modify Leveled lists (FCOM, MMM, FRAN, OOO, TIE, etc...). WAC Goblins, WAC zombies, skeletons, horses, and some others stuff are controlled here.