Every once in a while I find or I am notified of a spelling error in one of my quizzes. What do most people do in that case? I made the mistake of correcting the spelling of "anwser" and my quiz is still offline waiting for an editor. Is it best to wait until there are major changes or should errors not affecting the question be corrected as found?

Make the changes as needed - don't wait until something is 'major'.

If your quiz is still offline, this is probably just because you never resubmitted it to be put back online.

There's no need to take you quiz offline, to fix a typo, and then resubmit it to the queue. Edit the quiz as is, and then re-save it.

I've found your quiz in the queues; it's back online.

In fact, we prefer that you *not* take the quiz offline for a small change like this. Make the change, save, and then go back to your mailbox and mark the correction note "corrected". It will be checked by an editor, but it does not clutter up the queue. This also works for small rewording of questions and answers - changing "What was their first hit single?" to "What was their first hit single in the US?" for example.
If you end up having to change the whole question, then it is best to resubmit the quiz.