Well writing stories for just manga is really hard if you are not also a writer as well imo. It's also very hard for people like me and you here in America to accomplish such a feat. I also still want to work on manga's etc (I was apart of a group that's doing them still atm, but the boss was a dick to some of us and we split. I did writing/art) But I came to learn you can still go for a "manga" without art if you like, because it's still a story etc (I work in a light novel style when I write, and its fun) I would say just work on your ideas and write them out as a chapter by chapter basis. I'm not saying give up on wanting to be a manga writer/creator, but unless you become an artist yourself or pay a lot of money, you will never get something like a manga done. Just how it is these days though (As far as I have researched, but there are some artists who will come in and do it for free.)
But if you like, I am down to clown and work on a new group and have you be in it. I don't mind trying to get back on the manga route, its fun as fuuuuck. Plus I have a lot of stories and I can help you with yours as well if you like. Reply to me here or PM me if ya like. I also think almost working of short fics and such is also fun and gets fans. We can create "anthologies" of stories both original and fan fic (Trust me, theres a market for this online)
And working on projects with others is easy as long as everyone has the time to get them done and has space. A no pressure atmosphere is great and healthy in co-op groups like that.
(PPS, I have a fanfic oneshot on here plus a link to my RRL btw if ya wanna check out how I do things.)