Christmas Day Travel (Wise?)

Thinking of flying to SJU on Christmas day. Flights are significantly cheaper on that the sat/sun or before.

Ideally we'd like to be on Culebra. Is it possible to get Uber/tavlxi to ceiba, catch the ferry, get a rental car and check into an airBNB? Timing wise we know it can be done but aren't sure about Christmas day availability. Are the rental car places usually open, do the Airbnbs generally allow check in, does the ferry run etc. I've found some info like this but haven't been able to find all the pieces.

Also are grocery stores generally open Xmas Day?

Alternatively we could land at SJU that day and just get a hotel in San Juan the first night and then go over Saturday but we would lose a day there.