It will definitely work. I prefer using the SMS122 or similar pH controller to using a timer, especially on that large of a tank. It will conserve a lot of co2, and keep you perfectly balanced. Granted, CO2 is cheap, but changing it out frequently is a pain in the rear. If you have the money, I would definitely go for the pH controller. Also consider going for the 10 lb tank instead of 5 if you have the space for it. With the 5 on a 100gal tank, I would think you would be looking at refilling about every 5-6 weeks or so.
With a 100 gal tank I would also not recommend using a glass diffuser. You want to use a powered or inline reactor. If you went with a glass diffuser instead, you would need at least a couple of them.
Again, I would say if you have the money to invest, what you picked out will work great.
1 word of caution: Check your local CO2 supplier to make sure they actually fill tanks, and don't just exchange them. Otherwise, the first time you go to fill it up, you may be turning in your brand new shiny aluminum tank for something that is of much lower quality. If all you have a available is an exchange, you may want to forgo buying the tank online and just pick a used one up on your first trip to the CO2 distributor.