Check out what Orlando has to offer at Green Leaves Aquariums. He has really high quality equipment at great prices. As far as a method of getting the co2 into your tank there is a lot of good information on this site with a tank that large. Maybe wait to hear what others have to say.
With that large a tank you are in a different ballpark when it comes to getting enough CO2 in the water. A simple diffuser won't do it. A single external DIY reactor probably won't do it. And, getting enough water circulation all over the tank is essential to get the CO2 to all of the plants in the tank. I agree with Stevie that you can learn a lot by reading lots of old threads here.
But, another option is to go for low light intensity, so you aren't driving the plants to need a lot of CO2.
Let me tell you more about what I am trying to acheive.
100gal Open Top planted tank.Lighting will be 4 HOTH(54W) hanging hood , Substrate aquasoil amazonia and EI dosing.That would make it 2WPG.
For C02 I am planning BOTH together
1. Plan to connect the AM1000 and a EHEIM Compact + 3000 Pump below the tank.Guess I need to add IN and OUT lines for this and the Pump should run out of water(As per Eheim site).
2. I used the Eheim 2217 spraybar on top of a ceramic diffuser bubble stream to move the bubbles along the tanks length(before they rise up to surface) and got good results in the past. May not be as good as a venturi but misting definitely .
Tom has a Cal Aqua inline glass diffusor for sale right now. It would work perfect on your 2217, and give you the results you want for the second diffusor, while keeping things out of the tank and keeping maintenance down. $75 Classy, effective and a good deal. They are $110 new and I just bought one and then realized Tom was selling a brand new one. I would jump on that if i were you.
at green leaf aquariums check the ultimate c02 regulator and you can customize it with 2 co2 outlets. I use it on my 90 g. One of the outputs is set to 3-5 bps on the AM reactor and the other is used on a maxi jet.
I recall when we (SCAPE) checked out The Behemoth, Tom had more than a couple of the ginormous ADA diffusors at strategic parts of the tank. I think you should incorporate both mist and inline diffusing while continuing on Vaughn's train of thought: the right inline reactor at the right bpm should get your dissolved CO2 at your 30ppm target, while a couple diffusors and powerheads throughout the tank will allow you to target mist. While this would greatly increase the amount of equipment in your tank and may require a manifold, I think water flow and moving nutrients around is an easy step that leads to healthy tanks.