I heard playboy bunnies make great pets.
For about a week.
If you want an open ended learning experience, that will keep you occupied for the rest of your life, get an aquarium. The bigger, the better. I would not mess with anything smaller than about 90 gal. Maybe a 120 gal.
Much like reloading, you can make fish keeping as complicated and interesting as you care to.
Or you can just toss a few community specimens into the tank and observe the pretty colors. Much like shooting whatever Wallyworld has on sale.