1.
Can you be sure 3.3V will fully turn on your mosfet? There may be mosfets whose gates are designed for that, I don't know. But the ones I've used need something like 5 or 10V to drive the mosfet to its maximum conductance.
2.
The gate V is referenced to the more positive or more negative terminal, depending on whether it's N-channel or P-channel.
If you use an N-channel in the high side, then you need to guarantee the source (negative) terminal will see a clear path to ground.
Will there be a motor and another mosfet intervening? Then consider using P-channel devices in the high side. Then the gate will be referenced to the drain (positive) terminal. It will see a clear path to V+.
Either that, or boost the volt level at the gate of the N-channel device high enough to guarantee it will turn on.