I’m only just recently back - I went over for the Disneyland Paris Magic Run Weekend, and did the 36k challenge during the trip, in addition to the parks.
I would invite you to read my report from my trip over in the La Cava section of this forum - I captured a lot of my thoughts over there.
If you’re only doing a single day, my best advice for you would be to go mid-week and stay onsite the night before, get in for early entry (generally an hour and a half before regular open) and don’t be afraid to bounce around.
The hop from DLP to WDS is about twice as far as from DL to DCA, but it’s still a really easy walk. Given that you’re doing DLR and WDW both, you can easily skip both Tower of Terror and Rock 'n Roller Coaster at WDS - they’re both basically the same rides you know. Do make sure to spend some time in Toy Story Playland, and don’t miss Crush’s Coaster and the Ratatouille ride. They’re both fantastic.
Over in DLP, there is very little that’s a “perfect clone” of rides you know, most of them have some sort of a fresh twist. I happen to like the scene ordering in Pirates the best of the three I’ve done.
Lastly, don’t expect the back of the park to be open all of the way until Disney Illuminations (the nighttime show) - they will start to sequentially close things down an hour (or more) before the show, depending on crowds. That one surprised me.