my first tank was a 10 gallon, loved it , just make sure you do water changes often, you will find protein will build up fast and be sure to let your tank cycle for a while, being put your sand live rock and all in and let it sit , myself i let mine sit for almost a month before adding any fish. About when you asked about water adding , i use R.O water , reverse osmosis, when i can !! and i believe all of us here would agree on doing so! My tank consisted of a blue damsel, a 3 striped damsel, yes territorial issues did arise but it was not to bad if i had live rock on both sides so they each had "their own" territory. Since then i have had a 30 gallon with a sixline wrasse two clowns and a foxface lo that is getting to big for the tank. Wanting to bump up to a 75 gallon though as i have a horse shoe crab that is getting descent size .