Concept suggestions needed


#1

Hello builders world…i’m newbie John from Greece

I start making a project and i need your thoughts…

Watching this instructable video https://www.google.gr/amp/www.instructables.com/id/Underwater-Wrist-Thruster-185-Mph/%3Famp_page=true

i decided to make a small sea scooter board,on this board: https://www.gidivestore.com/eu/en/buoys/9723-sporasub-eva-board.html

:rofl::rofl::rofl::rofl::rofl::rofl:…but i dont know many things so i need your help.
I bought from their suggestions the following:

1.DT700 brushless motors: 2 pcs (i will run them parallel always at 30A,the easy way is to stuck the potensiometer to 30 A and use an run -off switch for the hole system but i dont know where to connect…Am i correct or …

  1. Kort nozzle for DT700: 2 pcs

  2. ESC speed controller 40A with BEC(i think from the price is garbadge…)
    https://m.ebay.com/itm/For-RC-Helicopter-40A-ESC-Brushless-Motor-Speed-Controller-BEC-3A-Accessory-/292583179808?txnId=1587784451019

  3. https://m.ebay.com/itm/RC-SERVO-TESTER-prova-servocomandi-a-3-funzioni-modellismo-auto-moto-elicotteri-/222569015914?txnId=2111217347012

  4. 10K Linear Slide Slider Electronic Potentiometer Module Dual Output Arduino

  5. Sony Konion US18650VTC6 3120mAh - 30A.I think that 3s10p is a good choice for about an hour runtime,

My questions:
1.do i need fuse?what A and where to place it?
2.which waterproof on -off switch and where to connect?
3.is it safe to use those servo tester, potensiometer and esc?or sth else?
4. What bms?with or without ballance etc.
5.all in a ip67 box or separate the li-ion pack from the esc?
Thanks in advance