I don't know about the wicking problem, but normally, we'll set the cement board just above the flange and then fill the resultant gap with either thinset or caulking just so that the flange won't kick the bottom of the cement board out. As for the hex tile (and unless you have something I haven't seen yet, it may be porcelain, but I doubt very much it's rectified-- I've yet to see rectified mosaics. They'd cost a fortune!) it should only add about 3/16"- 1/4" (with thinset) to the floor to set it over the tile you have now.

Use greenboard, and do the transition behind the swanstone, just before the edge.

Just a comment on this 10 year old post, but about 10 years ago, I had the same problem that the OP had - failed drywall causing tiles to fall in. I used cement board around the tub and shower and green board everywhere else. I didn't find the cement board much more difficult to use than the green board (or any other drywall) so I don't see what the OP's objections to it are. An interesting aside, this bathroom was not original to the house. The non-shower side of the room had been a closet wall (not a bathroom wall). I removed the "drywall" which turned out to be a gypsum board based lath 3/4" thick with plaster over it. On the back of the gypsum board was printed "patented 1885". The house was built in 1890. A cross section showed three layers of plaster between thin sheets of paper.

Am planning a bathroom makeover that will include replacing a small vanity top made of cultured marble. Does Corian offer integrated sinks in a different color than the vanity top? I know Swanstone does, but their color choices are very limited. For the counter I like Corian's Gray Onyx and Silver Birch and would love to do a white sink.