Yeah, me too on the anxiety! Even on line. That's one of many reasons I love this forum. People here are very kind and generous with knowledge. I've always felt welcome. Another thing is the knowledge base of forum members is vast and based on experience and science.
30 gallons is very good size to start with. Its big enough to be nicely stocked with plants and fish, and be forgiving as you stabilize the setup. . Corys do love to be in a herd and they love plants, so I think that's a great fish. I feed mine Repashy gel foods a few times a week and its fun to watch them swarm to it.
So Sunshine, welcome.