I can give you an idea of how to go about the first two, but for the UI......I'm going to start tackling one of those in the coming weeks so I'll show you how I did it (if it works
)later.
If I remember correctly, the matrix texturing commands allow you to texture each individual tile, which could simulate the effect that most 2d editors have with making the maps a multiple of 32x32 and using all 32x32 tiles. Then for detecting where to place each matrix, I remember a couple apps using an actual 3d cursor in the shape of a triangle or bolt or other object and whichever tile it was over was the one that was picked. Then you could texture it with whatever texture was selected.
For character tiles you could just use 3d planes, it's probably a good idea to limit your use of matrices to maps only because sometimes they run a bit slow if you have too many. You could make each plane the same size as a matrix tile, have all the planes at the same height, maybe slightly above the matrix, then it would be simple collision.
A good program to check out is MagicWorld, Robin King just released the source and it implements some of the features you're looking for beautifully.
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