I am 100% brand new to this hobby so excuse me if this is a dumb question. I recently posted about stocking for a 40 gallon I was looking at getting. However, I see the cost of a 20 gallon and its much more accessible for me rn with the space I have. My question is what can you really keep comfortably in a 20 gallon as far as full grown fish and corals? The main focus for the tank would be corals for sure so I'm fine if its only a couple fish but still. Will I have to upgrade rather quick if I only go with the 20 gallon?