1st, I'll just be honest and tell you you'll never get a rate like that on a
DCL cruise.
As far as what is included, the rate includes your cruise fare, port fees... out of pocket would be tips, excursions, spa treatments, shopping expenses and alocholic drinks.
As far as cruising with no kids--you'll hear some say there are tons of kids on board DCL, which is true, but having sailed several other lines, I didn't notice any more on DCL, except maybe my Holland America Alaska cruise (i don't think Alaska cruises attract families).
The kids are usually in the kid clubs or the kid or family pool. If you stick to the adult areas, you don't really notice them. I always had late seating so it was older kids, and I never noticed them at dinners.
Some things you would want to consider is what are you looking for in a cruise. Do you want a active night-life atmosphere, are you looking for casinos and more of a vegas larger then life feel? Then DCL might not be for you--since there is no casino, and its definitely not a party boat. They have fun on board--don't get me wrong, but it's not your "clubbing" atmosphere.. Which is what really appeals to me. DCL dining I think is very good, I happen to like the smaller dining rooms, and getting to rotate and have them be themed dining experiences. I enjoy the shows, they are geared to families and have a disney flare, while other lines are more like your vegas shows---Disney shows are musical/broadway production quality.
As far as ports it just a matter of wear you go, and DCL goes to a lot of the same places as other major lines, and have similar excursions.
As far as price, no one would argue that DCL is probably the most pricey of all the major lines. Partly because it's disney, and it's market share in the cruise industry is smaller, so they have to make up for that, and also with the lack of casino and less people drinking--they have to make up for onboard spending.
I have sailed Carnival, not a 7 day, and at the time I thought it was fun, but after sailing other lines I probably wouldn't do it again--at least I would never go on the Fantasy again--its yucky!! To me, Carnival is a bargin cruise, so you have to take it with a grain of salt. I would rate DCL number one, it offers what I like.. family atmosphere--a touch of class-- and a disney touch. Second would be Holland America.
Which room is best, depends on your budget first and what you desire. Best thing is to first decide what you can afford, and what you would feel most comfortable cruising in. Unless you get a suite, size is comparable with inside and outside staterooms. It's just one is a room with a view. As far as where on the ship, every ship as noisier rooms then others. noisy rooms tend to be above or below nightclubs/restaurants or by mechanical equipment, and a little research could clue you into which rooms are noisey.
As far as when to book to get savings---at least with DCL it's best to book early and shop around several different travel agencies. Unless you are a florida resident, booking later on DCL will just mean paying more. As far as time of year, it does effect the rate a lot.. Peak seasons--holiday's/spring breaks are the most expensive. Off-season--when school is in session, Jan/Oct are the best times to get bargins.
I have sailed at various times of the year, and its either very warm, hot or VERY hot. So you can always take advantage of water activities. Water temps fluctuate, but never to the point its too cold to go in. At least in my experience.
I would do your research. See what all the various lines offer, we are pretty biased here towards DCL, but all I can say is once I went on a DCL cruise, I never went back to another line!