Firstly we used a group choice activity which put students into groups according to their choice. Group choice is not included in standard Moodle but is available from the Moodle plugins directory: Activities: Group choice.
We then set various access restrictions for each weekly section. For example, here's how a teacher sees week 2:
In addition to activity completion and date restrictions, the screenshot also shows that students must be in the 'All at once' group to be able to access the section before 15 January 2018.
It does take a bit of thought to set up all the access restrictions. It's a good plan to have a test student account to be able to log in and check that you see the right items! We allowed users to change their minds in the group choice activity (Allow choice to be updated), thus it was easy to test both the options.