We took our DS at 8.5 mos and he has been 4 times since (he is now 28 mos). We are
DVC members and stay at mostly BWV or OKW. Our first trip was at BWV.
On the negative side, we have found that check-in at BWV is never on-time. I don't know what day you are going, and we often try to check-in on Sundays right about 2-4pm, which is a very peak time. We have had to wait several hours for check-in, often beyond 4pm. Hopefully that will not be your case, but just be prepared, as it seems you do have a plan. We just found it difficult - DS really needed a nap desperately and ended up having a diaper blow-out in the lobby while checking in.
DVC rooms are supposed to have pack-n-plays in all rooms. If they don't, call mousekeeeping and they will have one to you fairly quickly. Disney does have metal cribs which seem to come in 2 sizes - full size crib size, and smaller size (about the size of a pack-n-play). Both are off the ground and have nice thick regular crib mattresses (along with bedding which fits whatever size you get). We have requested a "metal crib" and have had good success getting them, especially at BWV. The smaller one worked nicely for DS, especially at a younger age. None of this will matter to you if your granddaughter sleeps in a pack-n-play. We found out on our first trip to Disney that DS did NOT sleep nicely in a pnp. We found out the hard way. The mattress is about one inch thick. Many many kids do nicely though.
Please note that we have been advised in the last few months whenever requesting a metal crib that the standard line is: "Disney is phasing out metal cribs, so they are few and far between to get." You can still request one, but who knows if you will get one. On our last trip, we didn't chance it, and ended up renting a nice full size crib from abbf.com. They also offer other baby equipment rentals if you need them. We were very satisfied.
Sounds like you have the formula situation under control. I believe Target sells even little plastic tubes of pre-mixed formula, but we are about 18 mos out of formula, and I swear things change ALOT in baby stuff in that little time. We flew in May and I definitely saw that they had signs all over that liquids were banned except for formula, etc.
We have not used the grocery delivery services ourselves, so can't comment.
Good luck and please post back on how it was!