It is easy to make the decision to purchase or lease a dedicated server, but that does not mean you will automatically know what should and should not do with it once you have it.
I can remember being a beginner and thinking I knew quite a bit about running servers after spending a few years managing a VPS. I knew very little about the difference between managed and unmanaged servers. What a surprise it was when I found myself completely on my own, handling everything but basic setup!
The best thing you can do for yourself and your future clients is to learn as much as you can and prepare before you get your server. Once you have it, you can still test and fail without any consequences to clients you do not have yet, but that will cost you money. That is the first thing you learn with a new server. If your server is not making you money, it is costing you money, and you want to at least break even, unless you have some mystery donor who handles your fees.
Fortunately, there are plenty of resources available for new server admins, including this very site. There are a ton of other people like you out there who have struggled already and made tutorials to walk you through things like reverse-DNS setup, closing open relays, and keeping your server secure.
You will make plenty of mistakes (hopefully not huge ones), and those first few months will take a toll on you and your social life. But in the end, you have the opportunity to reap the benefits for your business, organization, gaming site, or for whatever you plan to use your server.