Friends new boat pickup with a question

[bbtt123]

A friend of mine just picked up what seems to be an absolutely wonderful deal for $1800. Its a 91 19ft Bayliner Cobra with a 120hp force EFI. The boat was custom worked on with all new decking in the front and back, new carpet on the decks as well. Only work we can see is having to replace the floor board (easy) and just overall cleaning up the boat and wet sanding the boat to get the paint back to original. We do need to set up fish finders and hook up the bow mount trolling motor before we get on the water. Few questions though as I have never had to work on the electronics for a boat before.

First thing is the fish finders, he wants to set up two units for the boat, one bow mount and one dash mount so that we both have access to depth info in front of us while out on the water. Can we splice both units into the same sensor or will we have to run both units separately?

Second thing is the motor, we tried to get some turnover on the motor yesterday to make sure it wasn't seized, at first we got nothing but after a bit of tweaking (oiling the cylinders a bit) the motor spun freely. The bottom cylinder is showing a lack of compression compared to the other three, I know this could be a few things (rings or piston walls) but it seems to me with the motor being semi-seized (motor was never turned over for almost 2 years) I think it might be a stuck ring right now and the motor may need a decarb? What steps should we take to fix this (easiest first please) we can rebuild the motor but would rather try simplicity first.

Other than the motor the boat for $1800 is an absolute steal as far as I'm concerned. (thanks craigslist for the deals!)