If you think you'd like to use a wedding planner, then they'll definitely organise almost everything for you but I wouldn't think it's necessary to use one. It's just personal preference.
My advice to you would be to get a rough idea in your mind of a date, and then contact some hotels that you like, see if they have availability and go to meet with their wedding coordinators, who are usually full of advice and tips.
Once you know what dates are available at the hotel you want, then you can work from there with checking availability for a church if you're having a church wedding, and a band. They're the biggest things really - you'll usually be fine with things like flowers, hair & makeup as there are plenty of suppliers to choose from but the venue and the band can be the biggest things to try to pin down, so that would be my advice to you!
Don't worry - it's not that hard, to be honest! Or at least, it's as hard or as easy as you want to make it; you can get totally absorbed in wedding planning if you like paying attention to small details, or you can just book the important stuff and let the professionals just get on with their jobs, while you just turn up on the day!!