Re: Dojo Floor
My dojo constructed its new floor as follows:
Wooden framework around the sides. Inside this, a layer of used tires. Attached to the framework and resting on the tires, a lattice of 2x4's at about 14" intervals. Over all that, a plywood floor; then a protective tarp and a layer of tatami.
Ki Society style picks up the feet a lot and is very bouncy; tatami on a sprung floor like this suit it well. The downsides are that it's a fairly hard surface (making learning ukemi more difficult) and it was a ton of work to build. (Hint: measure your room at all ends. Our walls turned out not to meet at right angles so one end of the room was narrower than the other. This played havoc with the framework.)
Tatami have to be treated carefully. Store them either lying flat or standing neatly on a long edge, or they will warp. Keep dampness away; getting wet will ruin a tatami faster than anything. Ours are vinyl-coated and we hand-mop them nightly, but with attention to using minimal water, cleaning up drips promptly, and not letting water run down between. If there is any chance your site may leak, I would avoid tatami. Once they get soaked they are difficult to salvage. Also, even though they look portable they are very heavy; if you plan to move mats often I would get something else.
I believe my dojo has worn out 2-3 sets of tatami in 18 years. If you move them, they will wear out faster.
Most of the Aikikai dojo I've visted use a canvas tarp over some kind of stuffing (shredded tires in one case, I don't know about the other two). This can be vacuumed and seems easy to take care of. The weak spot is the grommets and ties that attach the canvas to the outer framework; these have to be replaced periodically. It's much softer, which is good for ukemi but has some drawbacks for footwork--you can snag your toes on it, and it doesn't bounce as much.
You may want to choose your floor treatment according to the needs of your style: how much do you emphasize light footwork? How much do you emphasize hard falls? Also, are you going to have to move it, or is this a permanent installation?