Lots of great info here already, but this is just my two cents from a WDW vet who visited DLR for the first time back in May (trip report in my signature).
- Can you get thru the park in one day
We had 4 days and were able to get through what we wanted in both parks in 3 days. We could have done it in two days if we wanted to push it. IMO, park hoppers are a must if your time is limited.
- Are all the parks connected
As mentioned, not connected but a very easy walk across a plaza to the other park. It made park hopping very easy and you do not need to go through security again. We definitely park hopped here more than we ever do at WDW.
- How much different is it from DW
Very different. DLR is considerably smaller. Small is good for being able to see and do everything in a shorter amount of time, but it leaves a lack of options IMO. By the end of day 4, we were getting a touch bored, especially in the evening. We never have that issue at WDW.
We also felt that WDW was more of a true "vacation" - when you step off the place, you can enter the "bubble" and exit reality for a while. With DLR, you need to find your own transportation, staying offsite is more practical for budgets, and its just not as "all inclusive" feeling. WDW is a place we'd go for a week on vacation, while DLR would be something we'd tack onto a California trip in the future.
- What is the best airport to fly into (coming from Ohio)
We came from NY and flew into LAX because it was the only city that had nonstop flights from our home airport. We used SuperShuttle to get to our hotel in Anaheim. It was fine, but long with multiple stops before they got to ours. I'd probably just take Uber next time. Other than that, we had no issues with LAX and the traffic was as expected.
- What about hotels? Would VRBO be a better option
Lots of great off-site hotel options in the immediate vicinity that are within walking distance. I would much rather stay at one of those than have to park or Uber from a VRBO/Airbnb. Part of the appeal of DLR for us was that we could just walk to and from our hotel with ease, which made it easy to take breaks and just take things slower in general. We stayed at the Tropicana which is a stone's throw from the gates. Its small-ish and motel style with exterior doors, but it was updated and very clean. Its no frills, but the price could not be beat for the location.