Re: Dojo Floor
Well, I would also pay attention to the height of your dojo's ceiling... I would imagine that small rooms tend to have lower ceilings, and 2x4s on tires plus tatami only allows for weapons work while on knees - although doing Kumi-jo in suwari could give an interesting twist to your training ;-)
Also, when any under-construction is not an option, I would pay attention to not use mats that are too soft. In my dojo we have a concrete floor, with tatami directly on top (ceiling!), so I bought the heaviest tatami I could get. Reason: when you fall on soft tatami, you basically fall "through" them and hit whatever is beneath them, so in our case concrete. The harder tatami maybe harder on you to begin with, but you get no surprise of falling "through" them. Also, harder tatami are better for feet, toes, ankles, knees (while turning). And heighten your attention to getting round ukemi fast.
Good luck with your project