You can book the trip right now. In fact I wouldn't wait to do so for a few reasons. First, the longer in advance you book the trip the better your chances are of getting the hotel you want and the dates you want. Let's face it, Disney is crowded almost all the time now so making advace reservations is the only way to go. Second, you can pay off your trip far in advance of going. I would usually make payments monthly, then pay everything off a couple of months before we left (I think Disney requires 45 days before, but I don't remember.) Now, keep in mind the new prices for the resorts only come out late August or early September for the next year, so you will only have an estimate on your trip, based on 2007 pricing. However, don't let that stop you. If you are going during one of the busier seasons, like spring break for example, waiting will only make you stressed out wondering if you are going to get what you want.
Now to the fun stuff. Since this is your first trip I have a few suggestions for you. First, plan the trip yourself. Disney makes things very easy to plan. I just can't see paying someone else to plan my vacation for me. I have been to Disney many times (9) over the last 15 years and have always done the planning myself. I have heard and seen to many horror stories about people going on the trip and things not working out exactly as they planned.
First, where to stay. No matter what anyone else tells you, stay on the grounds in a Disney resort. The Disney resorts are comparable price wise to anything else that Orlando has to offer, and with staying on property you get the keys to the kingdom. The perks that Disney reserves for resort guests are worth any price. For example, unlimited use of the transportation system. The off-site hotels do offer shuttle service, but you are on their schedule not your own and sometimes there is an extra cost involved. There is the Disney's Magical Express free shuttle to and from the airport, the Extra Magic hours for resort guests only where one park is open late and one early, as well as the famous Disney service.
The Disney resorts are classified in 4 different categories. First there are the value resorts. These resorts are the least expensive of all of them, and are geared towards families, especially with the younger children. The decor is really good, and each has a large pool with a food court. Of the value resorts my favorite is the All-Star Movies. Each wing of the resort is decorated in the theme of a different Disney movie. The food court is pretty good, but the rooms are on the small side with double beds.
The moderate resorts are the next step up. They are a little more expensive than the value, but also a little nicer in terms of amenities. They are bigger in terms of size as well as rooms, they have a little better food court as well as a sit down restaurant. Each has a big themed pool as well as each section usually having a smaller quiet pool. My favorite in this category is the Caribbean Beach resort. It is a little large, but much quieter than the AS Movies resort.
The deluxe and Vacation club resorts are the cream of the crop. The deluxe resorts are the best looking of all the resorts, are some of the largest, and have the most amenities. The Polynesian is by far my fav of the deluxe. When you walk into the lobby you would think that you were transported to a tropical paridise. The rooms are large, there is a sit down restaurant as well as snack shop. Plus, there is just something about being able to see the fireworks over Cinderella's castle from the balcony of your room. The Vacation Club resorts are pricewise just about the same as the deluxe, but are based on availability. The DVC members get first crack at the rooms. My favorite DVC is Saratoga Springs. I think this is the largest resort on property. Each DVC room has a kitchen or kitchenette, and are all considered home away from home resorts.
Each has it's good points and bad, and all come with the same great Disney service. You can't go wrong staying at any of them. I would check out the Disney website, www.disneyworld.com and use the resort comparison tool. You can look at the resorts side by side and then get a quote from them to see the differences in price.
When you buy your park passes, I would recommend you add the park hopper option to your tickets. The park hopper option is a little more expensive, however it is the only way to have the ultimate flexibility to your trip. Without the option you are only allowed to go to one park per day. For example, say you have spent the day at the Magic Kingdom, but then want to go to MGM to catch the Fantasmic night show (which by the way is a must see!). You are only allowed to do that with the park hopper pass. It just makes your trip that much more enjoyable.
There are tons of places to eat. My only recommendation would be to do a character meal or two. I always take my kids to the Chef Mickey's Character breakfast in the Contemporary. The food is pretty good, and Mickey and the gang each take turns coming to the table to say hello. It is worth it. There are tons of meals, table service and counter, character and non. Check out the Disney website and you can use the dining finder for more info.
I would suggest going to two other sources for information. I have already told you about the Disney website and put the link below. The other places I suggest are, first of all, the Disboards. The Disboards is a message board website all about going to WDW. Here you can get dining reviews, resort reviews, trip reports, tips on beating the crowds, all from people who love to go to Disney and know what they are talking about. Also, go to the book store and pick up the Birnbaums guide to WDW as well as the Birnbaums guide to WDW for kids by kids (if your son is old enough.) There are a ton of guide books out there, but those are the ones that have worked best for us.
Hope this helps, have a great trip!!