WinterBud A base of 50k words written needed and an upload rate > 7 chapters/week. Meaning that past the 50k words, if you have a stable update, you will one day enter the "trending" category. As for daily updates, it is still 50k words and just you posting a chapter. Those numbers are the one given a while ago but should still be relevant.
Also, the higher you are in the original rank, the better it is I think. There is also a number of ??k words written between two apparitions in the "trending" category but those ?? I have no idea. Probably 25k words I would say, meaning that for two consecutive times, you would write at least a little more than 3.5k words each day.