Cruise control issues are common and they say check all the vacuum lines under the hood. Follow the one that connects to the throttle body (atleast on the V8). It then runs up against the firewall and into some hoses that run up to behind and under the passenger headlight. People say that if these hoses are disconnected or broke cruise control will not work. Also, check all the fuses in the driver footwell as well as under the hood by the battery. Since its an intermittent problem and if you don't see anything obviously wrong with the vacuum hoses, then maybe something wrong with one of the switches on the steering wheel? Not sure.
Volume issues, not really sure but I would guess probably a defective headunit. Those are cheap and easy to replace.
Alarm for low washer fluid. I can only imagine its the sensor on the reservoir.
Seatbelt issue sounds like its all in the mechanism behind the panel. Either replace it or take it apart and see if anything looks broken.
As far as common electrical issues....Yes you guessed it. The WJ does have a *** load of "common" issues. Whats cool about these rigs is there are soo many DIY's and a lot of the things can easily be fixed in your garage. The most common electrical issue I know of is the broken wire issue that occurs in the drivers door boot. When you open the door all the way the black rubber boot that houses the wires that run from the body into the door. After years of use a wire or two in there split and cause all sorts of weird issues. They says its usually this one black wire that splits. Things I have personally seen happen due to this is interior lights don't go off, power windows dont work, door locks dont work etc etc. So none of the issues you mentioned seem related to the broken door boot wire, but could be worth checking into since its pretty easy to tackle.
The cool things about the WJ's is all you have to do is a quick google search and tons of threads and videos (youtube) come up with how to's. So do some searching for each issue and there is a good chance there is info about it online.