Hi @Nixiebunny, welcome to the forum! 
It’s always exciting to have more options in the marine robotics space, and there’s a special place in my heart for those with an accessibility focus that’s suitable for hobbyists and those in the STEM education space. Thanks for sharing your story and your ideas so far, and I look forward to seeing where this goes from here 
To clarify, is there going to be a camera that just records onboard rather than providing a live stream preview to the operator? If so I would note that there may be difficulty operating at depths beyond the distance people can see into the water, especially if it’s unclear where the bottom is or whether there are things in the water that the tether could get caught on.
You don’t seem to have mentioned anything about electronics enclosures. This thread may provide some useful insights from others’ ideas if you’re planning to make custom ones