American smooth is first and foremost a social dance style, and at its very core it demands the basic principles of improvisation, connection, lead and follow, etc. So it's about as far from a "sequence" style of dancing as you can get.
When presented in a competition format, however, it's understandable that one might mistake it for a sequence dance... Couples perform their pre-planned choreography, which can be very complex, and involve a great deal of side-by-side and obviously non-improvisational work. Of course, this is also true of International style, especially Latin. Even in Int'l Standard, couples usually have pre-planned routines.
In all 4 styles, the principle is the same: You typically start with a pre-planned routine, and then you adjust it on the fly when the situation (usually traffic) demands it. Sometimes this means simply altering your speed or direction, while other times it means altering the fundamental choreography, or even inserting some true improvisational material (eg basic patterns) before resuming the choreography. The biggest difference between Standard and the other three styles (Smooth, Latin and Rhythm) is that you're always in a position -- closed position -- that allows you to improvise immediately at any given moment. In the other three styles, depending on your choreography, you could get caught "with your pants down", so to speak.
But the best dancers can improvise and keep their cool in almost any situation. When dancing apart, they can use eye contact, or just have such a mental and emotional connection that they each know what the other will do. Sometimes that involves simoultaneous independent improvisation (ie each partner choreographs on the fly individually, without lead and follow), until they connect. Some couples will simply stop, wait for traffic to pass, and then resume.
At any rate, the point is, none of the above concepts are unique to American Smooth. It works the same in Latin. The thing that makes Smooth unique is that it combines the independence of Latin with the body flight and large, fast traveling movements of Standard. That makes smooth by far the most dangerous style on a crowded competition floor. (I should know... I was struck so hard one time, I was literally almost knocked out cold). But accidents in American Smooth are not as common as you might expect, which is a testament to the skill of the dancers involved.
As for the number of couples allowed on the floor at once, there is no official limit. Typically they try to split the heats at about 15 or more couples. The most interesting sight is a large competition (Ohio, Emerald, etc) where they do a 30-second "comparative Waltz", briefly combining all heats into one. That can be a zoo for sure. But for the most part, on a regulation-size floor, a 12-couple semi-final can move along nicely. Interruptions are frequent, but accidents are rare... especially if you're looking at the 12 U.S. semi-finalists.
Regards,
Jonathan Atkinson