Obviously schedule hasn't been released yet. Fantasy is your likely option if you want 7n (does a mix of Eastern and Western). For the Dream and Fantasy, the ships are the destination so I am not sure whether Eastern or Western will matter for you.
Start by looking at the trip reports, look at the photos, navigators, etc. It will help you get up to speed pretty quick. We did all of this prior to our fist cruise in 2010, and when we stepped on the Wonder, and it felt like home. Couple of really good reviews that are photo intensive. Look for Gambee's review of the Dream, LittleMissMagic's of the Fantasy. Both are awesome. I still go back to them for an occasional fix.
As for cabin, it really depends on your budget, family composition, etc. Haven't done a inside on
DCL, although I have seen what they pass off as an inside and oceanview on other lines. I don't think you can even compare the two. Didn't get the verandah thing myself until sitting out on it and overlooking
Castaway Cay. Now if it is in the budget it is a must.