Update: as I was posting I realized I could run WyreBash as its always been a cantankerous SOB. It told me two mods had mismatching .bsa files, so I unticked both, my game started up just fine. I ticked one, and then the other, MO2 dropped the attempt. I am unpacking those bsa's now, letting them loose to see if the mods involved work in my series of test characters I will be making. Oh, the joys of modlist making. lol