Starting my first SW aquarium

Hi everyone :) I just joined the site after coming across it while Google searching. I am starting my first saltwater tank, and I think I'm on the right track so far. I have a 20 gallon tall, with a filter, heater, and power head. I'm using a mixture of live sand and crushed coral as a substrate. I also have 11 lbs of live rock that I've added so far, and I'm going to gradually get more. I plan on setting everything up slowly, gradually building it up so I avoid any common mistakes. I just wanted to know if there was any kind of advice that people with more experience would be able to give me? Any tips are greatly appreciated, because like I said, this is my first time doing this and although I've done a lot of research, I believe you can never be too educated on something. I also wanted to get some input on what kind of fish to put in my tank. I don't plan on adding fish anytime soon, but I would like to consider my options since my tank isn't very large. I would like a few peaceful fish, as opposed to a single, more aggressive fish. I was looking at yellowhead jawfish and I really like them. Would a single one be good in my 20 gallon tall? If so, what else could I keep with it? Or is there something similar I could keep in there instead? Some other things I've been looking at are smaller species of pipefish, firefish, and chromis. I also really love pompom crabs and would love to pick out fish that would be okay with them. I am open to all suggestions. I like fish that are colorful, but I really like those that have a lot of personality. Any tips and suggestions are greatly appreciated. Thanks!