The good thing is that once the bookings open, you'll be able to see lots of choices available, and be able to choose three that work for you. (That part is a LOT of fun!) I am told that not ALL available choices show up, just some of them, so if you don't like what choices you are given, exit out and try again.
Also, make sure you like all of your rooms together so that you can reserve the room together. On the Disney ships there are a lot of veranda rooms, so if you really want only outside and inside, you might not have a TON of parts of the ship where they are together.
One other thing to consider, veranda rooms might not cost THAT much more (for us it was like 5% extra). It depends a lot on the particular sailing. So keep that in mind too. I know you won't know the exact prices ahead of time, but if the prices were close, would you want to switch?
Last thing, you didn't ask about a
travel agent, but keep in mind, even if you want to book it yourself, after you reserve the rooms you want, you still have a few days (I forget how many) to switch the booking to a TA if you want. We did this. That way, we had control of the initial booking and room selection process, but we got the benefit of the TA's experience for other aspects of our trip. Of course, it did mean booking airfare through the TA and paying through the TA, but it didn't cost extra.