I want to put the starting battery on #1 perko switch and 2 optimas on #2 perko. how would i hook the 2 optimas? pos to pos and neg to neg, then cable to perko? and can i gound with the starting battery?

Yes on the first and you should ground your stereo from the house bank. All your grounds should be on the same battery.

ok I have it set up with the large cable from the alt going to the "both" switch on the perko and the engine block ground going to the starting battery. Can I use the smaller cable going battery to battery or do I need to use the big stuff that comes from the engine? THanks

anything 4 gauge or bigger and you should be fine