Maybe somebody would recommend a mount strategy for my set up.

I was planning on going with three of the Dual DS 100's ($200x3 = $600)

I have a plan like this:

[17"][ 20" ][17"]
[17"][ 20" ][17"]

This would be cheaper, if it would work:

1 Triple DS 100 ($256) + Dual DS 100 ($200) = $456

The bottom 2 17" would sit on the desktop, the upper 2 would hang from the triple mount arm. The 2 20's would mount to the center pole using two single mount pivots.

Can you fit the triple mount arm and the two single pivot/mounts on a single 28" pole and base?