Oh, and to answer your entire floor of your home question, it would depend on the size of your home.

Our last house was a little split level house with only a kitchen, dining level, and living room, which would have been a good area for it to do at one time.
I have to break our current house into zones for the Roomba. We clean our kitchen most every night. I will run it in our family room. I will also either run it in the front of our house (living, dining rooms, and a large foyer). Other times I will break that down and run it in the dining room and then the foyer/living.
Depends on how dirty the rooms are. We have a zoo of pets and have LOTS of hair, which it does a great job on.
I don't know much about all the newer models. We don't have the base that the Roomba could dock itself on and recharge, but we could buy it as an option. I don't see the need since we have an extra battery so just switch off. I actually like that better than the dock idea since the 2nd battery can be charging while the Roomba is running and then it will be ready to rerun soon after using it. Of course you could have both the dock and an extra battery.
When we were shopping on Friday at Sams I saw a Roomba like ours with the dock and one virtual wall for $199. Seems like a good price even though you'd need more virtual walls than one and likely the extra battery.
I had a dream last night that my sister gave us a second Roomba, so Roombas are on my brain I guess.
