At least a 100.
Because it is a nice indicator that the author might be serious enough to continue the plot. It also is a good way to show that the story might be interesting enough for the author to lengthen it.
Lastly, I will check the release dates of each chapter, if it is a monthly release, I might as well just wait for the story to finish first.
For your 4-8 weeks indicator, a daily release means that it is at best 56 chapters...