On the subject of starting out tanking and anxiety over it. Just jump into low level dungeons explain at the start that you are new to tanking and any advice is helpful. And be open to advice. Most people are going to be understanding if they know you are new and are trying to learn. But if you don't say anything they are going to assume you know what you are doing and be far quicker to get upset if you make a mistake. So just be open about it at the start of the dungeon. Sure command missions could be nice, but I find doing dungeons with people and getting feedback is more useful.