If you want to go with the Mega 2560 board, then you'll have extra h.w. UARTs.
11.6V is a little high to power the Mega bd with, although it's probably indicated as
being within the allowable range. The problem is those weensey smt v.regs on the
bds will get hot if there is a large voltage drop across them, and the load current
is too high. Eg,
Pd = (11.6V - 5V) * 75 mA = 0.5 watt, which is about what those devices can dissipate.
IOW, not even close to 1 Amp.