Using the fiberglass fish poles i ran a couple of 2 gauge welding cable wires from the battery in the rear to under the console for the stereo. I have the under skinning as well and did it by myself with the boat on a lift in our boathouse. There's a small space when looking from the side of...
I've used the fiberglass rod set from Harbor Freight to fish wires when installing my stereo a few years ago. Worked great. I just taped the wires to the rods and pushed them to where they needed to go.
!5 pitch sounds like too much for a 90 hp engine. I think you would be better in the 11-13 Pitch range. When I had my 115 HP Yamaha, I went with 13 Pitch 4 blade Nemesis aluminum prop made for pontoons. It performed great.
On the fuel gauge, not much help since I never had a problem with any of mine. I did have to adjust the trim sensor on the motor to get my gauge to make the full travel. That sensor is really finicky. I played with it for at least 20 minutes before getting it right.