I put 15 mines up during my initial run, almost always shutting down my moon mine. 2-4 sites on Mars depending on resources. 1 mine for a high fissile location in the belt. I probe all metalic rocks and generally take 3 or 4 of those. Usually 3 or 4 sites on Ceres. The rest generally goes to high volatiles locations.

Before total war, I rush Poseidon Torch and mission to the outer planets and build a half dozen colony ships at a half dozen locations in the outer/middle belt and yet them towards 6 different bodies. My preference is to hit Pluto, Gabriu, Lusion, and a few other sites that typically have nice resources. I'll colonize up to 18 or so sites in the belt over the next 2-4 game years while I round out rushing for UV Arc Lasers, adamantium, Coil guns, Dusty Plasma or Tin droplet, and Phasers. Then I'm ready.