Welcome aboard, it spring so i have been a bit busy
1) w/s should be mounted on a strip of sticky back weatherstrip foam tape with screws holding the front down about every 10" if the dash is flat and not bowed down (different issue) this is sufficient and does not leak, look closely at the dash to see if it's sagging this may be the root problem.
2) I added inexpensive Farias to the parts page last week if you want to go that way
3) If (1) pitot has been removed I would be more worried about the lower pitot screw holes than the upper hose hole, I would replace the pitot & hose.
4) Typical sender issues but I would attach a jumper at the sender between the center post pink wire & ground, gauge should read max full, run across the lake & see if the meter still bounces or stays rock solid on max full, if it does replace the sender.
5) Dry boat, relaunch slowly looking for leaks, could be exhaust, rudder port, leaking fin bolt, etc
6) elbow grease, sweat equity
7) agreed

Rear center floor, that the motor box attaches to needs screws at least at the front
Always feel free to call with any questions 985-542-4336