Ah, I just read your other thread. You already have some plans and good advice. These pictures are in your 12v thread. I assumed you would be replacing that electrical wiring, due to the exposed copper and broken insulation. Don't re-use that trailer connector. The coax might be ok if it didn't get wet inside the insulation, but if you're in there you might as well replace it all the way to your radio The instrument multi-conductor wire should be able to be tested with an ohmmeter back to that barrier strip and if it is ok, then you could keep it. You just have to decide what to do about a disconnect at the step.
Any time you use splices or terminals of any kind aboard the boat, I would recommend crimped heat shrink terminals and splices.
You might think about using feedthrough fittings under there. That would make sealing the wires more reliable. Having waterproof connectors or wrapping a silicone (Rescue) tape around whatever connectors you choose is also a good idea.
Regarding the boat through the water speed vs. GPS, I like to have the paddlewheel for a couple reasons. As others have said, if you want the true wind speed then you need that data. It is also easier to determine your boat performance with through the water speed data and engine rpm. A dirty hull, fouled propeller, etc. show up quickly when you have through the water speed. No guesswork about effects of current that you will have with GPS ground speed only. I boat in Puget Sound, which has lots of current, so being able to compare is nice. Maybe it's not so important on smaller lakes.
Cleaning the paddlewheel is a bit of a chore, but once you get used to it, the water coming in briefly isn't so scary. The paddlewheel usually has an arrow to indicate which side faces forward, too, important for accurate boat speed.