M5.....I'll try to answer the question with my reasoning....for what that's worth. These micro baloons or sphere's are indeed micro, like I said in an earlier post this stuff is like talcom powder. You have to be extremely careful when you pour it and mix it or it will blow all over the place....hense the respirator.
It's not necessary to put it on the floor when you will lay down dynamat or equivalent and then carpet padding and carpet.......but it won't hurt it either. Once the mixture dries it's just as hard as any paint surface and you won't burst the bubble so to speak by stepping on it. Really no need to use automotive paint on the inside of the car, a good quality exterior latex house paint works very well.
Here's a few pics of my old glass body that I used this system on, my new body will get the same exact treatment.