You may want to consider getting a reseller account to begin with. This will allow you to learn the control panel, and to spend less time maintaing a dedicated server. Then, as you grow and decide that you want to stay in the hosting business, you can get a dedicated server.
Either way, you'll need an order/billing system, such as WHM Autopilot, ClientExec, Modernbill, AWBS (the old DRAMS) or for entry level purposes, you can go with something like whois cart, phpcoin, or write your own.
You'll need a way to process payments, and will need to either get a merchant account, or open a paypal account, 2checkout account, or other 3rd party processor account.
If you want to register domains for your clients, you'll need to have a reseller account with one of the domain registrars as well...most of the billing solutions mentioned above can integrate this as well.
This is just a start...there are a lot of things you'll find you need, the biggest 2 are time and knowledge. If you go dedicated, and are uncomfortable securing it yourself, find a management company who can do it for you. It's worth the price and you won't regret it. There are many tutorials that can help you secure it....but if you're the slightest bit concerned, get someone to do it for you.
Hope this helps