FOCBOX was not a 4.12, it was a design “based on VESC 4.12” which means firmware-compatible to 4.12, but it had much upgraded FETs over the 4.12 reference design.
FOCBOX (1.7) is a lot better than VESC 4.12.
Both can function just fine on a single XT60 for power, and an MR60 for phase output.
Did see a few posts in RC websites saying the 3.5 is a little lose hens my confusion to if it is a 3.5
FOCBOX was a single ESC (normal single motor 6374 that’s up to 65motor amps normally at max duty so battery amps will be lower)
it’s XT60 in to dule XT60 or XT60 in to a dule ESC I’m on the side of the XT90 (6355 x2 up to 110A motor amps even if it’s 2/3 battery amps 75A) what’s ther 90-100 degrees of the connector if you sustained it for 30 seconds up a hill?) yes the spe say up to 120deg but I prefer my connectors to not add to the heat in my encloser or passing heat in to my ESC
Yes I meant for a single [motor] ESC, correct
Nope 
Next build is 60A as well 