Welcome bagellis, yes you can have both. This diet is ultimately about calorie restriction on FD. However maybe you want to read up a bit on sweeteners as there are some controversial studies and claims out there. Good luck with the diet.

500 – 600 calories are yours to use anyway you like.
Personally I avoid caffeine due to it making me jittery, But I do drink green tea with lemon and stevia. I don’t feel as jittery with green tea.

One strategy I have is if I’ve stopped fasting for more than a week. My first fast day is typically liquids.
I like to get one of the meal replacement drinks that have all vitamins and minerals in it . With the chocolate flavored. And make a mix with a bit of milk and instant coffee. So it’s basically a Choffee that keep adding ice too. I personally make it bitter more than sweet.
I tried to use only that last year for a short period . My journal entries were indicating that I was going over the TDEE or felt hungry following a fast day no matter how much I ate. Making adf feel harder than iusing other whole foods on fast days So I only use the liquid days to begin nowas I can count on it every time. I just started using more fiber foods for breakfast when I break my fasts on feed days.