No, I don't have time to take that on, thanks. It's an interesting project, though, and it will be interesting to see how you get on.
I suggest you get the electronics and wireless stuff working as a mock-up to check whether it's actually going to be reliable enough for you before you get too far into packaging it. I mean stick the electronics in a bag, tape it to the paddle, stick your thumb over the pressure sensor and just see whether it controls the motor adequately when you're waving the thing around in a wet environment.
Given the application, I guess the throttle assembly will be in danger of getting bashed on things so it would probably be better to look for a flush push button to operate the pressure sensor, rather than a throttle lever. I think you will have to mock things up and see what works for you, but I suggest you try adding a slim housing into the outside of the tube, somewhere near to where you normally grip it, to contain the electronics. I'd look to make the housing with the section of a crescent moon that was a close fit to the tube, have a flexible water tight enclosure inside it to contain the electronics, and some way to remove it from the tube for charging. The biggest component it would need to hold would be the battery - perhaps a few AAA cells? If you include a QI wireless receiver you could recharge it inductively, avoiding resealing issues.
If you can't package it outside the tube then it should be easy enough to fit the electronics inside, but you'd need to provide holes in the tube for a pushrod between the throttle control and the pressure sensor, and another one to let the transmitter aerial out, and presumably both of these would need to be sealed. It feels like a neater solution, but harder to make and harder to maintain.