CCFL'S wiring in a series
From what I was able to find from Google resulte; this looks like a pretty straightforward power-supply decision.

I found a range of dkfferent CCFL inverters ($40-$350USD) for powering 1-12 CCFL tubes per inverter at lcdparts.net (looks like 6 tubes for $80 is their best price/tube for running your 6/12 tube setup you mentioned).

As for your AC/DC converter sizing, most of the tubes I'm seeing are 6W and under; so I'd recommend sourcing a converter capable of at least 8W per tube you plan to power.

This extra few watts of avail. supply should compensate for inverter inefficiencies, give a little power for your pulse drive circuitry for your phased signage image you're trying to replicate (BTW, I'm fairly certain that image was PhotoShopped), and help keep you fro  overheating your supply by running it too close to max output kf you end up uskng this project for extended periods at a time.