I'll answer a couple.
#1 - I have a 3 core with the serp belt and clutch fan. Close fit but it does fit, about 3/4" away. The clutch on the fan engages more when the engine is warmer, usually easier to rev or slightly quicker response, usually won't tear up the radiator on water crossings. Some radiators will sit slightly deeper in the nose for the extra room. Electric fans only work when needed, can have over-ride switches for cool down or water crossings, more efficient but can draw a lot of current, especially on start-up (30 amps or more). With the 3 core and clutch fan, my temp gauge never gets past 1/4, even dead of summer, mountin pass at 90*, or lugging it slowly through the woods.
#2 - Remove ground wire from battery and install test lamp between cable and neg batt post. If lamp is lit (you might have a little draw from things like clocks or the memory on the stereo), you have a draw. Remove fuses until lamp goes dim or out. That gives you an idea of where to look.
#3 - 3 lines, fuel in, fuel return, and vent. Don't know about the sending unit. Would have to look at a schematic.
It's just a Jeep, and if you don't wheel it once in a while, it's not even that.