CJR, ok just read this thread, sounds like a cool project. I was thinking about your desire for flare and I was wondering if you had thought about screwing the trees to a board? It keeps the big roots growing out instead of down and by doing that you get some butressing and flare. Like this one:
Well, I had a few seedlings, so I wanted to create something that you don't see all the time out of a BC. You know, the usual informal upright or the telephone pole with an osprey nest at the top standing in for a flat top. So, I bent a little movement into the seedling and I also screwed it...
www.bonsainut.com
You could lay out the whole forest on the board, screw it down, and let the trees fuse. This also keeps the roots shallow so you can get it into a thinner pot.
I was looking at the second swamp picture that you posted. I think the lack of knees is because they appear to be pond cypress instead bald cypress. Pond cypress don't tend to make knees as often as bald cypress.