The start is on the road in front of Paradise Pier, at the underpass of DTD, and the staging area/finish line is in the PPH parking lot. But that being said, if you stay Sat/Sun at the GC and exit the lobby to the road, you'll be right at the corals and ready for the start. It's just as easy as PPH and if you usually do bag drops, you really wouldn't even need to. And after you finish and get funneled around the back of PPH you can just cross the street back to GC. The expo will be at the DL Hotel which is at the end of DTD and if you stay there, you would just go through the side parking lot out to the road and back. So any of the 3 work well, it's all just a matter of preference.
I've moved once b/w the BW and DLH but we had a car so it wasn't that hard. And if you go from GC to PPH like the race, you would just exit the lobby and cross the street, it would all depend on how much luggage you have. Are you going home b/w WDW and DL or just straight to DL?
As far as relation to the parks, GC is closest and has it's own entrance into DCA. DLH is at the end of DTD, but close to the monorail and takes you straight into DL and specifically Tomorrowland. But it's different from WDW in that there's only those 2 stops ~ DTD and Tomorrowland. It's also where the expo will be, but since you'll already have your stuff from Fri, not a big deal. PPH is the furthest from the parks, but where all the race stuff is. We don't know what's going on w/ the 10k course yet, but if it's like DDD, the start and finish will probably be the same as the 1/2 b/c of the timing mats, but we won't know until later.
Personally, I really like the GC. I've never stayed in the DVC villas, but the decor is really pretty ~ it's all craftsman style, it's gorgeous. PPH is beachy and surfy. DLH is the original and classic so it's always special, each of the 3 towers has their own theme ~ fantasyland or Adventureland etc. There's also a lot of memorabillia in the lobby area.
And the biggest plus in the world for you, especially after Dopey, is that no matter which hotel you end up at, getting to the race is soooo much easier than the staging area/starting line walk in WDW.