How long do meatballs in sauce need to be heated in a crock pot

You don't need to add any water to the slow cooker whatsoever. Your recipe is somewhat similar to the one that I use to cook my lunches but the quantities seem larger than mine, much larger. I assume that you chop everything up into small piece, including the chicken. The slow cooker should not be more than 3/4 full, so reduce your amounts if the quantities are too big.

Chicken breast doesn't need more than three hours on the 'high' setting in order to cook (six hours on low); this cooking time leaves most of the vegetables crisp (courgettes and pumpkin soften, but bell peppers, carrots and onions retain their texture).

Running a kosher kitchen, I would not know about adding cheese to the food, but anyway I would recommend adding the cheese to the food prior to serving, not while it is being cooked.

If you wish to separate some of the vegetables, one technique which I have used successfully is to put these vegetables in a wire tray (I use the plastic punnets in which we buy fresh mushrooms): these vegetable are cooked like the rest but are kept separate.

If you do wish to add certain vegetables after you have already started cooking, then you are supposed to add 20 minutes to the cooking time (every time one opens the lid of the cooker, steam escapes and it apparently takes 20 minutes to obtain the same amount of steam).

Depending on the design, the heating coil may have collapsed and is shorting out at various points

This may cause it to run hotter than intended, and result in problems you describe

Measure the current with a meter and compare to manufacturers label, if much higher it's time to scrap it. Unlikely to be easily repairable if it has a heating coil

If it is running hot it is likely to fail soon and not heat at all

Modern crock-pots used solid elements, not coils. They also often have physical temperature regulation systems, not just a simple element selector switch