Correct. You'd need a CO2 bottle, CO2 regulator, 2nd pH probe, potentially a feed pump (that peristaltic might do it, or a tee off of your return pump manifold) plus media. There is another pretty large full CO2 setup in the classifieds as well.
Yeah, your tank is considerably larger than mine, and you have a sump, so CaRx is a viable option as well. Theres a **** good one for sale in the classifieds here for $100.
I'd use that unit with caution. Channel 1 on it has a ton of colors on a single channel, meaning you can't tweak the relative strength of the LEDs on the same channel, only dim them all in unison.
Yeah, I was going to suggest using an OSC statement. I think what you have there is correct. You can verify by looking at the chart that shows when your ATO is on/off.