As you discovered, it's easy in Arizona to take a class and pass the salesperson exam. To have an active license, however, you have to put that license under a broker. If you are planning to buy and sell on your own account, there are a few inexpensive places to work. Stay away from the fee split agencies and the Keller Williams model. You want a broker with low transaction fees and no desk rental or whatever they call the monthly fee now.
Real estate is tough to do as a side business. You have to show properties when people want to see them, and you have to work with title companies and lenders during business hours. You need to keep up with the market on a daily basis and and spend time selling your services. Continuing education is required to maintain the license. There are fees for the MLS, lockbox access, and for board membership. It adds up to a couple of thousand to get started and there are recurring costs.