Name your courseroom. We'll take it from there.
Five weeks, with the following one starting immediately. Since nothing separates one course from the next, a poor fortnight is never absorbed by a break; it becomes a backlog carried into a class that has already begun. Students who last in this format identify their difficult weeks several courses in advance.
A small assigned group producing shared deliverables across a course. The grade is partly shared, which is what makes a silent teammate costly. A written division of labour posted in the team space, where it is timestamped, is the single most useful precaution, because it makes commitments visible before anything goes wrong.
On when you post as much as on what you post. What is required is presence spread over several separate days, and one long session cannot demonstrate that however substantial it is. Across a five-week course these marks accumulate rapidly, which makes them both easy to give away and easy to win back.
The major piece near the close of a course, generally holding the largest single share of the grade. Because the final week goes on finishing and submitting, the real working deadline sits a week ahead of the published one. Reading its criteria at the start is what stops that discovery arriving too late to use.
Very little, and that is the point to plan around. A new class begins almost immediately, so there is no recovery week and no natural moment to catch up on anything left unfinished. The students who last in this format are the ones who identify their difficult weeks in advance and move work around them.