If you book a trip through a TA you will need to make all changes with the TA vs. calling WDW yourself. So it will depend on the type of planner you are - give specifics to a TA and sit back till take off time or checking and rechecking and want to be involved with planning. We booked through
AAA but I have kept her on her toes and had her make adjustments to our reservation - sometimes this was a pain as I could just have easily called WDW and requested a fridge in the value rooms, etc. but you can't (I'm sure she can't wait until we leave for WDW!!!) I also like to deal watch so that I know we are getting the most for our $$$.
As far as cancelling reservations - You can book 15 months out and you can make alterations to your trip up to the 45 day prior to arrival mark with no penalties (we booked w/no dining and then changed it when
free dining came along with no penalties/extra cost). When you make your reservation you are required to put down $200.00 and then final payment is due no later than 45 days prior. You can make payments or wait till end to pay off. Once you pay off the trip not sure how cancellation works but I know there are penalties involved. Check out
trip insurance as it covers some of that as well. We are heading down this October but I am already looking into October 2008 (won't be able to book till next summer but Already planning on saving and making payments so that it doesn't hurt the pocket as much as 1 big bill.)
This trip will be the test drive - calculate all costs - travel, food, hotel, passes, souveniers, etc. so that the next trip I will have a better idea of cost. We like the dining plan included as once you have paid off the trip - hotel, food (most of it anyway), passes all included in that price (also for some air) then whatever you bring for $$$ can be spent towards memories or things you want vs. the necessities. Do your research, book early, and then keep on it. Time passes quickly and before you know it it will be here.