Rue can be rough on the body when your not used to it, i would say don't stress your body even more by fasting, personally i like to sometimes dry fast the whole day, and by night time i drink alot of water and a light meal then i take rue, i find this way i get the benefits of fasting without the experience being too rough.
Not necessarily, at the beggining i couldn't drink the tea without adding alot of cacao in it, now i can drink 8g rue tea without any cacao or sugar, but it took months, some people handle the taste better than others.