Walt Disney World’s Magic Kingdom was originally based on Disneyland Park, yes, but MK is bigger, and the parks have diverged since WDW’s opening. Here’s a spreadsheet I created a while back comparing/contrasting which attractions are found in DL, WDW, and both:
http://spreadsheets.google.com/ccc?key=0AkAI9LTUaudtcGlybGh2anNZR0RPVHY2VGdkcWZWVlE&hl=en
If you’re familiar with Disneyland, you’re going to find copies of many Disneyland attractions at all the WDW parks, not just MK. For example, Disney’s California Adventure’s Soarin, Tough to Be a Bug, and Tower of Terror are found at WDW’s Epcot, Animal Kingdom, and Hollywood Studios (MGM), respectively.
For ticket discounts, there are some reputable ticket wholesellers; UndercoverTourist.com, MapleLeafTickets.com, KSG.com, OrlandoFunTickets.com. This late in the game, you’re going to want to pick them up at their Orlando offices rather than have them shipped to you. (You still have to order in advance, though). Also, the discounts are not large. Maybe $10 off the gate price, at the most. Do not be fooled by any advertisements for free or discount tickets you see along the way – 99% of them are timeshare scams.
I agree with others that Magic Kingdom and Animal Kingdom are your best bets. I don’t think the kids will be bored at Epcot – they’ve made it a lot more child friendly since it opened 27 years ago – but MK and AK are still the best for kids.
Haunted Mansion is perfectly fine for kids. It’s silly-spooky, not scary-spooky. Of course, you said you’re “very familiar” with Disneyland, and the inside of Haunted Mansion at WDW is exactly the same as that at DL, so presumably you should already know what it’s like and whether it’s okay for your kids.
The little manmade lake and boardwalk you’re talking about is, in fact, Disney’s Boardwalk. It’s located between Epcot and Disney’s Hollywood Studios. There are several restaurants there, both on the boardwalk itself and in the 5 hotels in the Boardwalk area. My recommendation there would be the Cape May Cafe clam bake buffet
Downtown Disney is not “under reno” as someone else said. Pleasure Island (one of the three sections of Downtown Disney), however, has been dismantled. All of the night clubs are gone. In its place are a couple new shops and restaurants. Downtown Disney is still the home of a bunch of restaurants, two of which are decidedly kid friendly – T-Rex and Rainforest Cafe.
Good luck to you.