This is a great question and one that I've had numerous teachers ask about. It seems like each teacher has their own style/ way of doing things.
Entering grades can be tricky when the class is self-paced and students are all over the map. One strategy I've seen work for teachers is to set benchmarks for where students should be by the end of the week. Then teachers assign a grade out of 10 or 20 points for the week's expected progress.
I've seen teachers categorize the exercises mostly as Classwork and use the Quiz Scores as assessment data. Have you ever considered creating your Quizzes through a playlist on CodeHS Create? This might allow you to make longer quizzes and get more data this way.
Thanks for providing the feedback here on offering more assessments. We understand that you want this data to be a clear reflection of student's mastery and understanding.