1. Live Rock, Live Sand, Small HOB, Powerhead, and a full cycle
2. Substantially different. Imagine maintaining the cleanliness of a pool where a handfull of dirt gets thrown in.....if the pool was the size of an olympic pool it wouldn't change the water quality very much. However, if the pool was the size of a cup mug of coffee it'd change everything. Same concept (terrible analogy,
but I'm not using the delete key this far in!) with nanos.....you really have to be 'johnny on the spot' and can't be "too busy for a water change, I'll do it next week".
3. I like my ten, but ask me in a month when my 20L is going.
........this is just my opinion.