I have one point to make about this setup.
When you boost a voltage from 3V3 to 12V at 400mA, you need at least 2A from the 3V3 source/battery, and more for peak current.
Depending on the type of battery you use for the 3V3 source, you will have a problem drawing that much current from battery. Even if you get that kind of current, the battery may suffer, and the life expectancy will be reduced.
I would have used a 12V source supplying the circuit, and made the MCU 3V3 power from that voltage with a small DC-DC switcher.