Let's see… there is no formal rule for them as much as we needed them at some point. However let me give you a few pointers.
First of all, E-chuuchuu has no universe, though several has been created.
E-chuuchuu stares mostly E-shuushuu users
Users are represented by their most used avatar or iconic. In my case it remains Kagami.
Event in E-chuuchuu are mostly canon, or are based on certain trait of our users.
It seems like I'm a rather normal person with common sense and facepalm at a lot of stuff.
Ran likes loli. He can change anyone into a loli with his lolification beam.
Smithy likes girl, and will change everyone into a girl with the kashimashi beam.
AngelLily is seemingly… angelic.
Evangeline is a witch nyoro~n
And so on…
Quality doesn't need to be high, but some effort on the text, framing, and extracting character is more pleasant to the eyes.
There is no format in particular, but I will say that 4-koma is very harsh for scenario. Really, I insist on scenario, make something funny for everyone, not some people on the board.
Personally I have no interest into making one at the moment mostly because I'm quite a bit detached of E-shuushuu at the moment. There isn't a lot of the old users of E-chuuchuu left so it's becoming more of a private joke between old timer. Doesn't help that I don't find any new user interesting plot wise.
I wish there was some more E-chuuchuu staying in the same vein of the old one. It can be made by anyone, introducing new users, but just in the same vein, I would be happy.
Merun @ Twitter - Doujin Shimbun