You are correct in feeding a battery to a MPPT, since the current is huge, it may take more than it can handle and smoke it...lol.
As for BMS in series, I have a bank of 4 each 12v lifepo4's in series, and the manufacturer states 4 in series is OK. I charge it with 60 volts just fine too. While from a matched battery stand point series electronics are not a optimal situation. I suspect in the end, it would be safer just to charge a battery bank and invert to 120 or 240 vac to run the EG4...thanks