Well, the answers to most of your questions are "what do you want?"
Best time of year--any time. Costs are lowest in the fall and in January/early February. Essentially, costs go down when school is in session. Fall is hurricane season. We frequently cruise then, but sometimes the ports of call change due to the weather. If you are willing to be flexible, it is a great time to cruise.
For a family of 5, I would suggest 2 rooms. That way, if someone wants to nap, you have a quiet place. You also have twice the bathroom space. It is frequently cheaper also. Again, personal preference.....
My
travel agent can get me the same deals on prices that I could get directly thru Disney. Personally, I like the interface with someone other than Disney just in case there is a problem. As to the "components" of the trip, you basically book the cruise, the air, and the transportation from airport to port. If you do it all on a Disney package, it will be more expensive than if you do the air on your own. However, only the items booked thru Disney will be covered on Disney
travel insurance. My travel agent has travel insurance available that will cover any/all components booked thru her. Why does this matter? Well, if you book the cruise thru Disney, then do the air on your own to save money and your flight is delayed/cancelled causing you to miss your cruise, Disney travel insurance will not cover the missed cruise.
Where can you save money? First, air fare if you are flying. Secondly, transfers. For a group of more than 3, it can be cheaper to book a van (there are several private companies) because they will charge by the vehicle, not per person. Thirdly, travelling off season. If you are driving, parking at the port is $10 per day. You can stay at the Radisson Port Canaveral on the night before the cruise and leave your car there. They provide a shuttle to the port. Another good "trick" is to drive over to the port and unload all luggage, etc. Then have one person drive back to the Radisson (10 minutes) and take the shuttle back to the port. Getting one person without luggage on the shuttle is easy. Just be sure that he takes his travel documents and picture ID along or he cant' get back into the port area!. The rest of you check in for the cruise and get in the line.
The farther in advance you book, the better. If prices go down, Disney will match the lower price (and issue a refund if you have already paid) provided it is requested thru your travel agent. If the prices go up, you have locked in at the lower price.
Have fun!
Kathryn