I understand the concerns of some collectors and curators in preferring unmounted prints. However, for me, having very precisely trimmed and visible borders is very important, something that just doesn't seem to happen with even quality 4-bladed easels. I, too, float my prints inside the window mat so the edges can be clearly seen. So, I trim and dry-mount. For me, the mount board color is very important, so I like to make that decision as well, and not leave it up to the customer/gallery/etc. I consider the mount board part of the artwork. (BTW, I trim the tissue to the exact size together with the print and have never had bleeding problems. These seem to have been solved long ago.)
I use Bien Fang (formerly Seal) Buffer Mount, which is reversible with heat, so I (or someone) could remove a print and re-mount it on another board (something I've only done when I made a gross error positioning a print on the board...). However, even if something does happen to the edge of a mount board, it is always covered by the window mat, so the presentation is really not affected unless something happens to the area immediately around the print. I hinge my window mats with linen tape with water-soluble adhesive, so the window mat is easily replaceable at any time. Of course, it should match the mount board.
No two of my prints are the exact same dimension, so I position each one individually. I usually tack tissue to a batch of prints (40 or so) to opposite corners, and then trim them down to the desired dimensions with a Rototrim rolling trimmer. I then set up to mount. Fortunately for me, my mounting is done in a very dry climate, so I really don't have to worry about drying prints and board that I've had around for a while. I use a self-modified T-square centering device that lets me position in two steps (basically a T-square with a reverse scale on the left part of the "T." I've posted about it somewhere here for those interested).
I like a little more space below the print than above it, but have a tendency to choose this by feel instead of some formula. I just move the print up from center till it looks "right." I then tack the free corners of the tissue to the board and pop it into the press (after dusting, of course) between two 4-ply rag boards with a sheet of one-ply rag paper covering the print surface. While the print is "cooking," I position and tack the next one. When I'm done tacking the print, it's usually about time to remove the first one from the press. I pull it out, weight it, and put the next print in the press. Repeat till finished