I think the most important problem is one that goes for any online team project, be it a manga, a game, etc. You all have real lives. All it takes is for one person to have a tough college quarter or a new job, and then progress falls nearly flat. This is especially prevalent when team members don't know each other personally in real life because there's less of a group bond.
Based on my experience, if there are no incentive for helping with this, then most likely there won't be anyone applying.
There's a lot of truth to this. To take it a little further: You're saying that you aren't a good artist, so you'll need other artists. Okay. Then you say you have the basic premise, but you'll need people to write for you. So what is your job anyway? Supervision? People rarely band under a person who just has an idea unless they've proven themselves. Because everyone has ideas. I'd go so far as to say that many talented manga artists already have their own manga ideas. Is your idea good enough that they would rather work on yours?
I'm sorry for being discouraging, but realistically speaking, the likelihood that this will run well is just not very high. If you do manage to gather a team, I'll really be hoping for the best for you guys. It's just that I've just seen too many people start up projects online and never finish, and it's discouraging for me too.
