Being freshly rebuilt I'm going to say 130 to 140 lbs but you wonder about things like the gearcase. Might want to have your own mechanic give in the "once-over"
Whoa, so many things to correct.
Let's start with the low voltage issue. Do you have an electrical meter? You need to trace your battery wire connectors and see if their maintaining voltage along the way. Do you have wing nuts on your battery? If so replace them with nuts. Might be your nutruel...
Pop off opens at high speed so yes that could be it otherwise clogged water passages on the starboard side.
Sound like the past owner knew there was something wrong and Mikey moused it.
I use the steering wheel puller like you have on the upper left hand picture. I tighten the heck out of it and give it several big taps with a large size steel hammer.
I personally liked me the champions but many on this site like the ngk's.
Click on this site and click on your model number for all the parts. Good luck.
https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1996&hp=70