My preference would be to use 2 batteries
a single battery with a 100a BMS can only deliver 100a to an inverter's load
2 batteries in parallel with the same 100a BMS can deliver 200a
no mention of what inverter so I'm assuming a 12v system
generally a LeFePo4 is limited to 100a continuous discharge (some less, some more) (never a good idea to constantly push the limit)
also consider the inverter's efficiency
so if you have a 1000w load it's possible the inverter will have to draw 1200w
at 12v that's 100a
a single 100a BMS discharge isn't going to like it
with 2 batteries the draw on each would be a sweet 50a to the BMS(s)
and with two batteries, if one fails you still have a working system