Try the Bubly sparkling water drinks. Really good flavor, with zero calories. Especially the new orange cream and lemon cream that aren’t out yet, but should be soon. I got to try them because my sister works for them.
For the record, I stay away from anything processed or with “natural flavors”, including those. But since you’re already drinking gatoraid, it may be a suitable replacement for you.
Although IF does increase your metabolism relative to continuously eating throughout the day, the effect is relatively small. If you’re at a significant enough calorie deficit to lose weight then “breaking your fast” with a small portion of Gatorade is unlikely to affect things much. I probably would stay away from calorie-containing foods and beverages because of the other benefits of fasting, though.
If your Gatorade is sugar-free, don’t sweat it (pun intended). You’ll hear conflicting opinions about artificial flavors and sweeteners but the evidence against them is minimal, and in my experience it makes no difference whether I have them. YMMV, though.
I wouldn’t at all worry about vitamins. They don’t (usually) have calories or flavors anyway, unless you’re ingesting something like gummy vitamins. I also wouldn’t worry about water with the juice from maybe half a lemon, which would only be a few calories and not enough to interrupt fasting.