I agree that it is never too early to start planning.
If this is a first trip, I don't think I'd do a cruise. Like others have noted, while there is Disney magic in going on a Disney cruise- the real magic is being at WDW or DLR. i.e. I'd make my first trip one that is primarily devoted to the parks. Case in point...one of my good friends went to WDW for her daughter's sweet 16. It was said daughter's third trip to WDW. My friend suggested they do a Disney cruise for her high school graduation gift and her daughter turned down the offer saying that she'd miss the parks...i.e. she'd be on this gorgeous ship with all kinds of Disney things around her, but would be missing the biggest things that make her love DIsney vacays. So.... they'll be returning to WDW for a standard park trip.
Next things I'd do is buy a good book. I like the ultimate guide since it covers everything from the parks and dining options to lodging both on and off site. It's a HUGE book, but it's very helpful and can clear up so many things. I had 12 WDW trips under my belt before I bought one (got it to plan my girls' first trip) and it was mind blowing and eye opening. i.e. how much I just didn't know.
That right there is also a big issue. It is typically cheaper to stay offsite, but there is a lot of value staying onsite that isn't something that is fully measurable in dollar figures. You might save hundreds to thousands staying offsite, but you also miss out on the 24/7 magic/service (intangible, but actually a huge deal), EMH, 180+10 dining booking, DME, free parking (or ease of Disney transportation right there), etc. I also believe that time is $. I spend less time in transit if I'm staying onsite + EMH affords me more hours in the parks. So, you could stay offsite - spend the same amount on MYW tickets as me who is staying onsite - but I get a lot more park time b/c I'm onsite. Still, onsite is not for everyone...and it's tough with a party of 5 w/3 adults- so you may find condos offsite that suit you better.
I would strongly recommend looking at Mousesavers and reading over the historical discount charts and the rack rate info. The discounts are no guarantees, but it can give you a good idea of what to expect. Also, while
free dining is a better deal now that dining prices have increased...if you plan on staying deluxe and have a 35-40% room only discount- it's typically a greater savings than free dining...and no worries on room only since those can be converted into packages while still giving you the room discount.
The forums are a wonderful place to get info, but Allears website is a must for anyone planning anything Disney.
7 and 4 are also really nice ages to have a first visit...i.e. things are still pretty magical. There are lots of fun things to enhance the magic as well, like character meals, pirates league, BBB if either are girls (although I guess they do a prince pkg), etc. So at least you have time to research all of these things.
There are many ways to do a WDW trip the right way and there are a wide array of budgets out there for everyone's ideal average trip. Air will also play a huge role in travel costs. At least you have the luxury of time which gives you plenty of time to save.
Finally, if you decide to stick with the cruise option you could do a land and sea trip so you get some park time before and after the cruise. You might also check the cruise section of the forum to start getting ideas from the cruisers posting in there.
