JS,

If you are intermittent fasting there is not too much care you have to take for what you do when fasting. I personally still apply fasting rules when I fast intermittently, which is nothing goes in your mouth but water.

Yes, supplements will get you out of Ketosis, worse, it is called partial eating and your body is going to rob your reserves to compensate.

Your muscle cramps is a magnesium deficiency. When eating take magnesium rich foods, but add 400 mg magnesium twice a day with or after meals. I prefer taking ionic magnesium liquid with fulvic acid.

During your fast don't take anything but filtered water.

Archus