Well, let me tell something about what happened with/to me a year ago. Someone had an idea for a 'crazy fun mod'. I liked it so I joined. At last, we had 5 people who wanted do go for it. It quickly shrunk to 3...
These 3 went on. Well, after a while all 3 where still there but only one really worked. Not me...
So at last we decided to stop it. It was not gonna work.
You see, we had no idea, no plan for the mappack. Well, a vague idea, a sort of concept but we never detailed it and never put on paper what our goals were, working kinda isolated, only now and then sharing some maps. That was all. After a while, we had no will to map for it anymore. It was no fun anymore and we didn't had the idea it was really important no more...
Well, I'm not that experienced modder, I can only tell fromthis experience now...
So I want to say: know what you're doing from beforehand. SunTzu said: A good general wins the war before the troops engage... A bad general engages first and seeks victory after that...
So: plan it first...