I had a very enjoyable weekend taking out some of the early 90s install in my van, but I am a complete electrics novice so I am back on here for ANY pointers and advice!

Well, at one time It was an autohomes campers but all was ripped out and an ok-ish (cough) MDF refit was done (my profile shows the current before pics

Right, so there is a cable running into the water tank. The sink is not attached though, but I found what looks like an electrical foot pump loose behind the unit that will power the tap - this is not attached to anything, pipes are all easy peasy, but what about electrics? I have one cut wire sticking out from the wall behind MFI sink cabinet, and I guess two points on the footpump thing for wire attachments... Can I just extend this cable to the foot pump, and whats the deal with earthing all this elctric/water mixture?
Also, I have fitted a nice old fridge, but how do I go about wiring this into what seems to be a minimal electric system? Should it be directly from the main battery? do I need to add a fuse box/switching system into all this danger Im about to get myself into?
As you can tell, I *really* am looking into electrics for the first time.