The RedSea unit would not be very cost effective. You would be refilling your cylinder more times then most would care to.
You would at least need a 5lb cylinder. My advice would be to get the largest cylinder you can fit.
Filling a 10lb cylinder will run you 15-19$
Filling a 5lb cylinder will run about $15-17.
it depends on what type of plants you plan on growing. if you're going for high light demand plants, you will definitely benefit with going pressurized, especially with your tank size.
i agree with orlando, go with the largest co2 tank that you can afford. you can get one from either a fire extinguisher supply shops or (where i get mine) from a beverage supply shots. i prefer a beverage supply shop, because after the initial cost for a tank, when your tank is empty you just return it and swap for another. and you only pay for the cost of a refill.
the initial cost to set up a pressurized system is daunting for people of limited means, but you do save in the long run. with a 10lb tank, you would have to replace/refill every ~6 months, as opposed to every 1-2 weeks with DIY.
With a big tank come a big filter.
Have you decided on what you would like to get?
With big tanks I prefer large media filters, for example an Ehiem 2260 or 2262.
Those are big plug and play filters that move a ton of water.
You will most likely want to utilize a reactor for co2 diffusion. Or you could opt for a needle wheel pump for this as well. Both are fairly inexpensive to find. The reactor being the least and very easy to install.
i have a huge wet dry filter on this system. I also have 10 pirahnas. So water changes are a must. I need help with co2 systems. I need a good regulator and want to know if I can use a glass diffusor or do i need to use a reactor? Also can I put the reactor in the sump?