I am a long time DL goer and have started visiting WDW in the past few years.
1. It's huge. HUGE.
2. I was sweating like crazy in October.
3. I find it oddly cheaper than DL. For me, from Vancouver, Anaheim is obviously closer but flights are actually often cheaper and the WDW hotels seem to have more selection and better deals.
4. You need to do a little planning. Online Fastpasses for some rides are necessary - depending on the day, waits can be very very high for some rides. And if you want to eat at be our guest (beauty and the beast restaurant), you really need to plan ahead.
5. I have a great time. It's not as cozy as DL, and I struggle with the weather at times, but I'm very much a west coast native lol. I love Epcot and Animal Kingdom, both which are unique to WDW and I think very much worth a visit.
Hope that helps!
1. Agree. Each park is (or at least certainly seems to be) larger than both Anaheim parks put together. And the only two parks that are anywhere near each other are Hollywood Studios and Epcot. If you stay on property, transportation everywhere is free, but it takes a while to get from A to B to C.
2. Yup.

3. I think this is going to depend on what you're opting for in terms of lodging. Disney property is going to cost you anywhere from a little to quite a bit more, but there is a convenience factor built into that.
4. This one I disagree with quite a bit, but not how you might think... You need to do a LOT of planning.

DL/CA can be a very unplanned, off-the-cuff sort of trip and you'll be able to fit everything in without a problem. With WDW, you have to plan, plan, plan, and plan some more. Then when you think you're done, re-review everything only to realize you didn't plan everything.
5. While the parks are definitely different, and layouts are different, there are similarities. I love Test Track (Epcot), but Radiator Springs Racers is WAY better (same technologies but very different stories to them). The Haunted Mansion in DL is superior when it's decorated for Christmas.
Disney World is a very different animal than
Disneyland. In fact, the first time I visited DL I didn't even realize I was enjoying myself until a few days in because I was so used to having to over-plan everything! lol
I think you have to understand your party as a whole, what their interests are, and then probably talk directly with others in a similar situation that have done WDW (or possibly both) for tips and pointers.
Also - one of the things I was most disappointed about was going to DL two January's in a row and enjoying beignets every morning in DL but then returning to WDW and ONLY being able to get them at ONE of the resorts!