For a no fish cycle, you can just toss in a single small shrimp that you purchase from the grocery store. This method will take weeks to complete. Doing it with fish will be faster, but it is hard on the fish. The uneaten food as well as the waste the fish make will help with the process. All you are doing is trying to get the nitrafying bacteria to grow. However, I'm used to saltwater, not fresh water. We have live rock and fresh water doesn't have that. So I'm not 100% sure on what goes on with freshwater.
As for saltwater though, the larger the better. The more water you have, the more stable it will be. My tank is about 120 gallons in total, maybe a little less now that I got rid of the refugium part of my sump that I made. The Key is patience and husbandry. If you can let the tank fully cycle with clown fish or damsils, then keep up with a weekly 10-15% water change for the life of the tank, you will be golden. My issue is the water changes. I just can't find the time to shut the tank down to do a water change. This last time was water. My Anion resin in my 3 stage DI was depleted and I needed to replace it before I made anymore water, and I had to wait for funds to come in, then the time to change it and now, I have the water, but I have not added my salt to the barrel. I make about 45 gallons of water at a time so it takes a while to mix and heat up.
Anyway, if you want more information on salt water tanks, post a reply in my saltwater thread. I don't want to jack this one anymore than I already have. I will give you all the information that I have on the subject.