Lots of questions!
Yes, your cruise ticket includes your room, most entertainment, and most meals; however, it is NOT all-inclusive -- that's a common mistake. Some people (usually the drinkers) run up onboard tabs higher than the cost of their cruise! Expect to pay extra for meals at the specialty restaurants (Most large ships have 1-2 fancier, upscale restaurants, which cost $20-25/person/meal -- that's on top of the meal you've already paid for in the dining room.) Expect to pay extra for alcoholic drinks, Starbucks-type coffee drinks, and sodas on most cruise lines. Obviously, it varies by cruiseline, but you might expect to pay $2/can of soda, $3/beer, and $6 for a mixed drink. These drink prices are true for meals and between meals. Also expect to pay for whatever you choose to do when the ship docks at the various islands. Finally, expect to leave room in the budget for tips; on the last night of the cruise you'll tip the waiters who've served you all week -- expect to tip $100-150/cruiser.
Now, the good news: Aside from tips, these "upcharges" are all optional. You can eat every meal in the dining room or the buffet (or order from room service -- it's free, just tip the waiter who delivers it to your room), and you'll pay literally nothing for food. You can bring cookies and fruit back to your room for between-meal snacks. You can drink water, tea, lemonaide, and plain coffee for free. On the islands, you can just walk around town, grab a cab to the nearest beach, or just stay on the ship and hang out by the pool. Basically, cruising is like having kids -- within reason, you can spend as much or as little as you wish.
You'll find PLENTY to do onboard; however, it varies widely. You'll have to investigate the various ships to see which one appeals to you. Plus you'll stop at islands, which'll offer a wide variety of activities. You're more likely to leave the ship saying, "I didn't have time for this, and I definitely want to do that next time."
Recommend a cruise line? I've done Disney, and it's wonderful -- it's also twice the price (yes, really) of the other lines. We prefer to cruise more often!
We live close enough to drive to Port Canaveral (roughly in the Orlando area), so we limit ourselves to ships that leave from that port; it's MUCH less expensive for us than airfare X 4 people, so that's our "starting point" when we're choosing a cruise. Next, I'd look at the size of the ship. We like the big ships with more activities. Then I'd look at the islands where the ships will stop. We like the ports with watersports and activities; other people look for shopping, etc.
For a first cruise, I'd suggest that you choose a four-night trip. Three nights just isn't long enough -- you're barely on the ship. But seven would be miserable IF you turn out to be one of those people who gets seasick. We did a four-night first, and it left us wanting more -- that's much better than doing a seven-night and wishing you could leave mid-way. And though it's not true of the majority, a few people just don't like cruising.
