On BP? Well, it started out with Darius doing everything and I learned to FRED from him (basically trained up from scratch.) Our only other FREDder is Axem who is, well, Axem. So our FRED team is actually pretty small compared to something like ED, which has something like 6 or 8 FREDders but no firm overall direction so they don't know what to do.
My advice would be to get a small group (2, 3 or 4) of FREDders who know the lore intimately, have firm outlines to work from, and receive prompt and strong feedback from the rest of the team at every stage of drafting the mission. Quality over quantity, and direction really helps - you seem to know what you're doing storytelling-wise. The drought isn't so much a problem when you only need a few good designers to get a strong campaign done.
I don't know about the idea of having a starting crew and a finishing crew. I think there's something valuable in having the same lead on a mission from start to finish and only tag-teaming stuff like bugfixes. But it could work well!