Q: How much "provided substantive feedback to classmates" is enough?

A: All participation posts need to be initiated by the student receiving the points.

For DQs they almost always want 2 posts minimum, each post worth 5 points.

For design assignments at least one, worth 5 points.

I shoot for 150 to 200 words, sometimes less, sometimes more, depending on the material being responded to. A dq feedback response to another student might not require as much. A design might have you supplying feedback, referencing links and going into more detail.

All participation posts should be made within one or two days after the assignment. I often see someone logging in on day 7 to do all the participation. I talk about this in the announcements. That kind of response isn't helpful to the person it is being made to as it is to late to apply your information to their work, and it'll cost a couple of points here and there.

The end of the week critiques are more about formal critique writing. You can be more informal for mid-week feedback. Pretend your best friend has asked you what you think of their work-in-progress. Add a second pair of eyes to the equation. Be helpful and supportive, but stay away from "good job" generalities. On ground I do rapid crits that are 2 positive comments and 2 critical comments. Even if you love something and have nothing critical to say, explain why you love it.