Having just worked my way through part of your questions, I think I can be helpful here. I don't know if my little screen shots will show up here so I have a attached a Word document.
To allow students to resume a lesson, click on an existing TaskChain and then click on Edit Settings. These same
settings are available to you when you are first setting up the TC. If fact, TC seems to remember the settings from the one previous set up, so these settings will like show up by default.
Under Entry Page, make sure that Attempts is chosen.
Also under Attempt Restrictions, Permit Allow Resume.
This will result in the following window for students who are returning to a taskchain. They
can resume their last attempt that is in progress. (See the link on the end of
the last attempt in progress.)
There are similar options for each task when you click on edit chain and then
edit individual tasks. I have stopped using these. They seem to simply allow a
student to use F5 refresh while working. Probably not a problem when you are not counting their scores.
This feature has made life a lot more live-able for my
students in lessons where I permit multiple attempts. It permits them to pick
up where they have left off when a lesson has been interrupted by the end of a
lab or otherwise.
A couple caveats. It only allows students to resume their last attempt. They also can't resume a lesson where they have looked at all the tasks, perhaps gotten feedback and then simply wish to improve the scores on items they did poorly on.
Resume has a couple of things my students need to get their minds around. I hope to put a short tutorial together to help deal with the many questions that come along here.
For your second question regarding student review of scores, I am not an expert but I expect
that the answer is in Review Options which is at the bottom of the menu when
editing individual tasks. Get there by choosing edit task and then choosing an individual task. I haven't played with these settings much though. This can be a time consuming process if you have a lot of tasks.