Hi,
1) For every volt the gain is 2.2, so a 1V signal becomes 2.2V.
2) Yes.
3) (50A * 0.15R) * 2.2 = 1.65V
Work the other way round to save time on "iterative calculations": (0.75V/2.2)/50A = 0.00681R.
I'd guess the closest single value current sensing resistor you'll get is 5mOhms. You could add 2*1mOhm to a 5mOhm but I don't recommend that much, maybe my fussiness is unfounded. Maybe paralleling a few e.g. 3*20mOhm or something but I'd use one single resistor, unless your making it/having it made.
An expert here with more experience on current sensing resistors may be able to suggest how to get 6.8mOhms in a useful way.
Does the input have to be between 0.7 - 0.8V or that is the maximum? If the latter then a 5mOhm should be "ideal" = 0.55V at 50A.