Subwoofer recommendation for swarm

How do you distribute the subs? Can they all be on the same side of the room or on just two walls?

mkgus, a DSP designed for bass management will work fine. The subs can be placed anywhere in the room. I think against a wall or in a corner is best as this placement increases efficiency. I would put the two front subs in the front corners and the others anywhere. Ideally if your crossover is low enough a mono bass channel is optimal. With a swarm system I think it behooves you to use a cross over below 80 Hz and as Duke suggests use a steep curve, 24 db/octave or higher. If you are using a DSP bass management system I have seen crossovers as steep as 80 dB per octave which I actually think is too steep. The speakers do not blend well. 48 dB/oct is the steepest I would use. If you put them all along the front wall they may actually overwhelm your speakers. It is always OK to experiment. Just leave yourself extra wire until you are sure of the placement. 

How do you distribute the subs? Can they all be on the same side of the room or on just two walls?

Well mine are just on two walls and work just great. I've moved them around experimenting a bit but with my system its almost impossible to have one on each wall. Well I could by putting one or two up near the ceiling! Which by the way according to DBA theory would be better. In practice however mine works so well I just can't see going to much effort trying to improve it.

Mine are on the left and right walls, each one a different distance from the corner. Plus I have one powered sub almost exactly in the front left corner. None of these is localizable, to the extent I often times have to touch the cone to be sure a sub is really working. Really low bass is amazing- it sometimes is so diffuse you feel the whole room immersed in it, yet other times its imaging the drum or bass guitar precisely on the stage right along with everything else. Seamless.

Tim aka noble_100 has a room almost identical to mine (one foot less each way) and he went through a very definite procedure to locate each one, which as I recall resulted in one very near each corner. 

Remember speaker location is only half the equation. The other half is listener location. The other 50% as Yogi Berra might say is having four.

I'm looking at buying the 10 inch subwoofer kit with the external Dayton amplifier.  Which driver is recommended, is the one that comes with the kit a good one?  The price is nice the stock way but I have wiggle some room for better drivers. I'm planning to buy 4 of them. Any thoughts? 

Bigger is better. Bigger magnet, bigger voice coil, better faster response. Bigger cone, more bass. Bigger box, well you get the idea bigger is better.

That said, impedance and efficiency are important. Especially if you will be driving all 4 off the one amp, then you want to be sure it will be able to drive them all at once. With mine, thanks to having two amps I was able to compare them wired for 4, 8 and 16 ohms. While they deliver more power into 4 the bass was much better by far at 16. According to Duke none of his customers who have compared have preferred 4 ohm. Something to keep in mind when comparing speakers.