Install Linux Mint. The pros of Debian ecosystem minus the cons of Ubuntu.
As an example of stability: It is the only OS that still runs fine on my computer more than 1 year after it was installed. No other OS remained so much stable in my experience even after regular updates.
Make sure you install the latest Mint, if you do (I have heard that distribution upgrades are a pain).

How do you ask a question to the instructor? If they only provide forums, sometimes other students will answer them for you -- but they are not necessary qualified. How can a student bring up tangential topics that may enhance the class?

An instructor always has the option of answering the questions posted in the class forums. For example, in Coursera's Automata Theory, Prof. Jeffrey D. Ullman used to reply to a lot of queries himself. For such a subject, unbiased explanations were very essential. Further, the prof's responses ensured only legimitate doubts were asked and quality of discussions were maintained.

So I guess it also depends on the professor.