You have the math correct. 3.2 is about the lowest you want to discharge the LiFePO4's to. For most of their discharge they are at 3.4 or 3.3 per cell. The bad news is that they stay there being almost flat in voltage, then die really, really fast. Almost too fast to realize your pack is getting low, and to give you time to get on the ground. And that can permanently damage them. So it is good for a flight pack to size it bigger than you would ever expect to use in a day.

I used to solder NiCads all the time, but the lithiums (either kind) are VERY sensitive to the heat, and it is extremely easy to damage them. Best leave it to the pros with the right equipment. For ground support stuff, I would think that a AA spring battery holder would be good enough - but I haven't tried one to see if the cells fit.