Showgirl, just go for it - use WordPress (most popular) or GeekLog (slightly more obscure and a little harder to get to grips with, but well worth it), jump right in and play around. That's the best way to learn anything, and also the best way to determine whether or not you'll need an administrator.
You can always decide whether or not you need an admin later on (if you do, be sure to consider my services.
). For the time being, just have fun.