woofer combo & alignments: on large vs few small

The Multiple/small configuration can be as applicable as a single large.One large:pros 20Hz bass,cons- have to do with settling time and speed as frequency increases.Small/multiple:impedance usually isn't an issue,multiples can have similiar radiating area,lower distortion (each driver has less excursion),faster recovery time,smaller box (relatively speaking),better in-room distribution of bass.Con:usually don't go sub 20Hz the way a 15-18-24" can.
Never been a big fan of side-firing.Integration/phasing is more complex and sometimes leads to unusual bass nodes-depending on room characteristics.Just another $.02.-MO.

The bigger woofer does not have to move as far, but has a harder time moving at the same time, the smaller woofer has an easier time moving as a unit but a harder time maintaining this as it has a longer distance to travel. The enormous research into cone material of the last 30 odd years have been directed toward this problem of cone linearity. The classic distinction was smaller woofers were faster while bigger ones went deeper. This has been greatly blurred in modern designs. Theory aside, you can get good results going either way. I would focus on the sound of the particular speaker as a whole, not the size of its drivers. The virtue of the side firing driver is in great debate, as was pointed out above they increase the problems of integrating the sound in your room.

Actually it is simple, when a big woofer barks the many small woofers yelp and run away with their tails between their legs ;-)

When woofers are at play,the smaller goes to and fro while the larger over-shoots the mark.In packs,there is safety in numbers;>