I was in the same boat as you. I was curious about adding a tank to my Iwata Smart Jet. I didn't have patience to evaluate and buy all the necessary parts (the number of choices is staggering).
So, I bought a Sparmax Air Tank System. It has received excellent reviews in Europe but is not available in the U.S. for some reason. So I contacted Sparmax and bought one directly from their HQ in Taiwan. I paid $125 including three-day shipping (will arrive tomorrow).
I really don't have a problem w/ my Smart Jet, but want to experience a tank so that I can shoot at a really low psi. Since Sparmax manufactures Iwata compressors, I said to myself, "Why not?"