Got our accommodation booked today… BLT 1br from Wednesday to Monday! Hoping that’s a decent choice for marathon purposes but I have no idea how transportation works so just going with the flow!
You got great advice above so nothing earth shattering to add, but I've done CR for my two marathon weekends (and some other race weekends) and enjoy it as a race weekend home base.
Buses pick up and drop off in front of the convention center, so a small walk over from BLT, but not really material.
We usually rent a car but would always do the buses on race morning which I never really had any big problem with. Although for the 5k and 10k this year we drove and I think I liked that better on the margins - could better control the time, parking is easy, and you can leave at your leisure. CR/BLT share buses on the return with FW and WL so takes a bit of time to eventually get back. This is pretty minor though, I could easily go back to just bus and be perfectly happy.
Monorail for the half and full has been flawless so far (knock on wood).
One thing I did this year that I enjoyed - taking the monorail back after the half and full. Grabbed a coffee and one of those big donuts at the Joffrey's right by the Epcot monorail entrance, several other runners were doing the same so the monorail ride made for fun conversation with other runners and curious guests, and I found the extra walking/keeping moving helpful.
Assuming the weather is warm, there's something nice about lounging around either the pool or marina areas during the day with the quiet vibes of Bay Lake.
One either pro or con depending on your park habits and bedtime - MK fireworks are at 8pm that time of year, which is at least reasonably early if you'd like to watch then head to bed, or if you're in the park and then walk back. I'm boring and try to be in bed 7 to 8 or so and inevitably end up sitting there listening to firework booms while I'm trying to fall asleep, reciting the whole show in my head. I'm probably on the more early side of bedtimes though, and all-in-all it's a non-issue.
The Electrical Water Pageant is at CR/BLT around 10pm and it can be pretty loud if your room is facing Bay Lake so may be an issue for light sleepers, but probably a non-issue for most.
You may be planning to cook/eat in your room with your villa, but if you are looking for resort dining, don't sleep on Steakhouse 71 To Go mobile ordering as an alternative to Contempo Cafe (which I don't enjoy as much in recent years).
Sorry for the long reply!