Simon said it all, but as youre going to run 4200mAh cells, your biggest concern will be the long runtime.

If the boat isn´t overpropped, it´s the runtime that will cause massive heat build up in your motor, which will either fry it after a few runs, or permanently damage the magnets due to overheating over a longer period.

Adding a simple aluminum coil the the can is the first thing to do, adding brushtab cooling is better, ast that´s closest to where the heat is generated, the commutor.

The pics show a 700 motor, but the principle is the same.

The inlet sketch shows a tube glued into the hull next to the prop, on the right side, viewed from behind, facing forward.
Sand it flush with the hull, you can do without the extra drag from things sticking out from under the hull...

The outlet can be on the side close to the motor (short lines less friction), or, better, in the bottom, facing towards the transom, creating sucktion, sanded flush like the intake.

This is a pressureless cooling loop that wil always function and cause minimal drag.
As the hull will be sealed, there´s no airflow, so cooling the ESC is always a good idea.

Let me know if you have more questions or need more pics.

Regards, Jan.