yeah i have the same enter key on my keyboards
for the aluminum problem it is not one by itself, it will just form a Faraday cage if you use a metal plate and really greatly reduce range, if not completely prevent transmission if the transmitter is too low power.
when i say it support both, you can't have both at once you either solder the iso switch or the ansi one.
iso is 2 things you need to pay attention to on the plates, the vertical enter key and the shorter left shift or split left shift.
the GMMK Pro is not out yet so it may or may not have it and yeah it will not be low profile out of the box, but i do not know if it would or not support LP switches.
And at last the input lag, Logitech are pretty much the undisputed kings on that, they use a proprietary protocol optimized for latency while pretty much everyone else uses plain old Bluetooth, and well Bluetooth is not optimized for anything,