Looks good. I've been thinking about how to turn the inverter on and off independent of the SBMS in my system as well.
Since the EXTIO3 is creating a short circuit when it's "on", then if I wanted to manually turn off the inverter while it's not in use, I think a SPST switch (SW4 on your diagram) on just the EXTIO3 positive line (green in your diagram) would function as a manual off for the inverter.
It has the added benefit of not being able to turn the inverter on if the SBMS detects an undervoltage condition (empty battery).
The SW3 switch should work as-is, but it could also be on the EXTIO3 positive line (blue) going to the BP100
The charger should also work fine, but if you wanted something silent, check out MeanWell's LED drivers. Adjustable voltage, fully potted, and no fans.
What is the B2B Votronic device? If it's a way to charge your Lifepo4 off the engine's alternator take a look at Renogy's DCC50S, it combines the MPPT with a DC-DC charger, but there is nothing wrong with your current setup.
What software did you use to create this diagram? Looks nice!