Oh, and one more word on commentary-based groups. IME, the most important thing about the members isn't that they're "close to the same level" or even writing in the same genre. It's that they all share the same honest goals for their writing.
People who just want to write and don't care if they get published, but still want to write well are great in a group together. A group who want to produce good indie books are great together. People who want to hit the NYT bestseller list are great together. People who just want to get that contract or an agent are great together. People who want to improve their fanfic are great together. But when you start mixing these goals in the same group, it gets really, really hard to comment because you're not as focused or knowledgeable on what will help make that goal. It's natural to fall back to your knowledge, which is reasonably focused on your personal goals.
For instance, in one group, there was a wonderful lady who was writing her memoirs of being a child during the Great Depression. It was wonderful, delightful stuff and we all enjoyed it. However, her goal of publication was printing out a few copies and giving it to her children and grandchild. Thus, any advice on how to make it more dramatic, more marketable, more whatever was pointless because it wouldn't help her achieve her goal.
Another example: A different group I was in had a guy who could only write when he had "literary orgasms" (not kidding, that's what he said), and was devoted to penning fantastic prose first and foremost in order to tell his tale, even if it took years, even decades to get it right. The same group had another member who normally penned 3-5 books a year. They were both published, both nominated for Hugos (different years), but their goals were seriously not the same. (That group was very dysfunctional, kinda destructive if you didn't fall into one of those two writing camps, and didn't last long.)
Something to consider, at least.