For the forum I would say perhaps a role-playing part although most people won't use it, but if you get more members you should. You should have a questions and answers board so people with questions can ask. You should also have affiliate buttons so you can affiliate with other sites. You should also have a staff section so you or the staff don't need to PM or e-mail each-other to change, suggest or add a rule and also to discuss member behaviours and site changes etc. To have a release section in the forum as well since some people might only go on the forum and it's always nice to have an archive for releases and to have contests maybe to encourage members to do something or another or just for fun like a holiday contest when you draw and create something for the site and submit it and then people vote for the one they like best.

That's pretty much it.

EDIT: You should also have a games section when you actually play games like wish corrupter and the who what where game, posts to a million etc. and a place to spam, just post stuff like your wish-list or your adoptables.

Ummm... You just set rules such as:
1. Don't copy other peoples characters
2. Don't Power-Play or God-Model or just giving yourself infinite power so that you could destroy the world.

those types of rules then when people RP they just have to follow the rules or something happens to them...

I'll get on the staff section later , The rpg can wait for a little while

Go to forum widgets in your administration panel. RPG is a widget and can be added very easily. Customization is also simple. Just need story and whatnot.

You should also have a section for art and stories so people who have any can post them.

I don't really think THAT one is necessary, since this is a forum for manga?