My best advice is to simply call and book directly with Disney.
If you book online, the actual policies regarding cancellation and such are the same, but it's much harder to make changes later if you need. If you do it all by phone, you can call and control your whole vacation. If you book online and then need to call and make a change, there are a lot of extra hoops to jump through (including not being able to simply transfer the deposit over, you'd have to pay another one while the first was being refunded).
If you want the most flexibility, just call yourself. Just the fact that you are here shows you know enough about Disney to be able to do this; their agents are well trained in dealing with newbies, and if you're here you can do it yourself.
Good luck!
NED