Even if the motor is not quick change, you can still reach down there and release the two tabs on either side of the motor and remove it from the base to see if the impeller is clogged, or will turn freely by hand. Popped breakers could be in the wiring, rather than the pump. If you can reach the connection at the pump, disconnect them and run the brown and the black straight to the battery to test the pump.
As far as the threads go, if you have a ball valve screwed straight to a through hull, then you will have a mismatch of threads on both ends of the ball valve. Both the through hull, and the live well pump have straight threads, to accommodate the backing nut. The ball valve has tapered NPT threads on both ends. Therefore, my main concern would be how many threads do I engage? If I used any sealant, it would be a paste, rather than tape, so that the threads will screw in further.