Wanting to build a sub able to dive to 200 meters, and speaking about how easy it is to build a narco sub.
With 200 meters/600 feet crush depth a pressure hull would have to be made of thick special alloy steel, probably with internal braces. Portholes as well as all openings in the hull for pumping water or propshaft seals are weak spots and should be avoided or kept to a minimum.
May consider to make the boat lighter than water, probably with some exterior ballast weight that can be dropped without using pumps in an emergency.
Pumps able to empty ballast tanks under 200m pressure will have to be special ones, should also be capable of more due to clogging, unintended greater depth etc.
Salt and fresh water have different density and viscosity. Consider silt or floating stuff entering the pump intakes and so on. Pumps fail all the time.
Leaving the boat at more than 30 meters without diving suit will probably kill you.
You did not specify salt or sweet water, speed, loading of batteries and a hundred other things. But my chrystal ball tells me that you cannot be that old, at least your reaction is childish b.t.w.
