I followed a 1200 calorie diet, lost like 28kg. I do not recommend it. It can destroy your metabolism and cause serious damage, which happened to me. I've gained back about 7kg so far and over a year since starting it, my metabolism is only just starting to recover. So I'd aim for 1500-1800 cal. As for eating back calories, no, I don't when I'm trying to lose weight. I feel like it's kind of redundant if I do.