actually jerkymotion, that is looking like a nice plan. very well thought out. that drawing is almost identical to how i started! there are some opamps and a reference to be able to measure the full scale positive and negative. one for each X and Y, just like you have. then you will realize that you must mix the two signals together to get the motor response. so in your block diagram add another single box with both arrows pointing to it and label this box as MIXER. then you have the option on how to develop the output. you can use locked anti-phase (as you are implying in your drawing) or you can have sign-magnitude method. for your drawing, the output of the mixer has 4 outputs, but two of them are the same. A and B (two A's and two B's). if A and B are run simultaneously at 50% duty cycle your average motor speed is zero. for clockwise rotation, then duty_A > duty_B. for counterclockwise then duty_A < duty_B.
in between the mixer output and the H-bridge is another block with the name "gate driver". we can talk about that when you get there.
and please, add anti-parallel diodes to each of your mosfets. the motor would blow up if you tried to run it like that.
keep working on it, you will get there.
Mr.Cool