That’s a difficult one. I usually will only have 3-4 books going at a time, of that. I updated one story on a weekend basis, as it was one that needed more writing. As for my other stories, they are often text fic and or short/one shots, so they are easier to get a chapter in even if it’s short.
At the moment I am not as good as I was at updating, primarily because I’m tired. The advice I can give you is to have one out of the four that you fully dedicate to a certain day, say Saturday. Use the other days to spread out, you don’t need to update everyday! If you have texting fics (which I think you do if I read correctly) then I’d use them for, if you feel needed, regular updates and leave the buffer stories for a set day.
For your drafts, I have about four, some that are ready to go and some that I’m holding off because I know it’ll be too much to keep a track of. I’ve already posted more than I can juggle, so my advice there is to try not to outstretched your time. Keep your draft a draft until your certain what your writing, and even have a few chapters ready.
I hope this helped.