What Pages Should I Create?
As the wiki's name might imply, this wiki is made for creating pages for your gang members to allow people to learn about them.
You can make pages about existing characters from a fandom; it's no problem that they're likely on another wiki. This will let everyone learn about these characters without searching all over wikia to find the wiki they're from. Pages for your OC gang members are also something you can make, because it will help other MBers learn about your OC(s). Alternate personalities count as gang members as well.
However, don't make pages about your MBer self. I believe the Scholastica wiki is better suited for you to do that.
I don't think that Spirit Animals (for the Spirit Animals message board/SAMB) exactly count as gang members either, but we can discuss that later.
How Do I Want Pages to Look?
You want a good description of your gang member, of course! In other words, give details about their appearance, personality, powers and abilities, anything you think is needed!
There are some parts of a page that are absolutely necessary, though. You definitely need a good, fleshed out description of the gang member the page is talking about. People are interested in their appearance and personality, so give them that!
Go here for the details you want on your page.
Hey, That Gang Member Has the Same Name as Mine!
That isn't a problem. You and the creator of that gang member's page either have the same character in both your gangs or your gang members share names. No problem at all. Contact them on their message wall and work out how you're going to distinguish your pages. But whatever you do, don't do anything to their page.