I've been wondering about doujinshi (amateur Japanese comics), and the process that it's made. How many pages is an average doujinshi? What's the average size of the book? If a doujinshi circle is involved where there is more than one artist (ie: CLAMP) then how many pages can a doujinshi be?
I know not all doujinshi are fan-comics. For those that are original stories, are they usually self-contained or an ongoing thing? For fan-comics, how exactly does that work in the US if you want to sell a fan comic without getting into legal troubles? I realize you can get away with it in Japan, but I'm not sure about in the US.

Also, what is the process in which an doujinshi circle is formed? Does everyone draw their own comics then combine it into one anthology kind of thing? or is it a collaborative effort?

From my extensive knowledge of hentai, I can tell you that there is not set number of pages, or issues. Most seem to just be self-contained short stories based off of something made by another company, with an occasional sequel or series. I have no clue how rings work, but I assume it's just people working together on one issue or more.

I know that you can sell fan made comics in America, but theirs a lot of things you got to look out for, and laws to abide. Thats why fan comics aren't popular here, becuase if they became to popular, then the orginal makers would try to find a way to sue or stop the maker of the fan made comic.