In the course level you can enroll users with a fixed enrollment period. See Enrollment Fields in https://docs.moodle.org/28/en/Upload_users#Fields_that_can_be_included for details.
Activity overrides per user is not yet a common feature. The quiz supports overrides and you be able to manage access to other activities by way of user completion of the quiz. Have not tried that myself, though.
hth
Personally I do not find it necessary to argue about what's intuitive, outside a philosophy seminar that is. So for me it's not really the question what Moodle's default is, but rather whether there is a setting to apply the desired behavior. And I agree that the behavior you desire is reasonable in the context and should be available by settings or some other way. You should open a tracker issue for this, if it doesn't exit, and invite interested parties to vote for it.
Try adding !important to the width rule, something like:
width: 150px !important;
See if that enforces your preferred width.
hth
Plenty of ways. You can use activities such as the Glossary module, Database module or the contributed Dataform module. With the Glossary and Database you can populate the content to the course page by way of their auto link filter. You would have to add the item names on the course page, e.g. in a label, and the auto link filter will link each one to the actual content that in your case would be the item url. With the Dataform you can actually display the content (and or any subset of it) on the course page either via a block, a label-like resource or the Dataform instance itself (you set it to replace the activity link with the actual content. hth