There is no substitute for cubic inch or in this case surface area

My listening room is 20'x15' with wooden floors (with an 8x12 carpet) and windows. What I don't want are woofers that are so powerful they rattle my windows and shake my floors, adding bass distortions.

I have a pair of Sonus Faber Olympica Nova 5s with three 7" woofers that go down to 32 Hz. They are perfect for my room. I can feel the vibration on really low sounds and various percussion like tympani, sticks, and snare drums sound accurate. I can also hear placement and depth.

Prior to these I owned a pair of Golden Ear 2+ speakers. They had two 5" by 9" subwoofers and two 8"by 12" planar bass radiators. The bass was not nearly as accurate as my Sonus Fabers. I could turn the bass up and down, but if I turned it up too high my windows rattled and floor shaked. So, accurate with sound waves that are felt by my body is about as much bass as I want.

My main towers are 15” Altec 604C coaxial. 

My sub is the floor firing 15” Velodyne. 

Imho in order to project authority, you need to move a lot of air. 

...And then some.

https://youtu.be/iGa9259pz-I

How does sound stage and woofer size go together? I thought that is more a characteristic of mids and highs. 

I think of multiple small woofers only in the sense of how HIGH they can go. Given the same volume (moved air), the key to me is that I can run an 8 woofer much higher than a 12", potentially allowing a much simpler 2 way crossover with all the potential negative impacts from any part in the signal path. 

What I don't know is if (given the same air move volume) if four 8 inchers can reach as far down as a 12" (SPL at low frequencies, and resonance frequency). 

Directionality increases with frequency.  Larger midranges will be more directional so placement matters more.  My experience has been that I prefer speakers with a smaller midrange.  They tend to have more even in-room responses.