Sounds like the wires are for the oil flow sensor. This is a notoriously problematic little thing, but easily sorted by dismantling, cleaning & reassembling. There's a little rubber diaphragm in there which senses when there's no oil, or the oil flow is slow, normally due to the filter gauze being blocked. It should light up the 'oil' warning light in the monitor gauge if it's disconnected or indicating low oil flow or no oil. This will put the engine into guardian mode.
There's a water level sensor in the cylinder head - some of these had water temperature (overheat) sensors built in and others had them separate. They can also be problematic, but easily changed - held in with 2 screws.
I'd say you need a 15" pitch prop on a 4.8m RIB, provided you're not running it heavily loaded. If you find you need a 16" pitch, I have one here in very good condition which you can have for £40.
