Yes. According to the CDC, all passengers traveling to the U.S. need to have COVID tests (taken no more than 72 hours before travel). For more information on the CDC regulations please visit this page: https://www.cdc.gov/coronavirus/2019-ncov/travelers/testing-international-air-travelers.html#general. We recommend that everyone be prepared for the possibility of staying longer in the case of a positive test. Anyone who would like, can get tested at Blue Holbox (the wedding location) for $130. Here is a guide for other places in the Riviera Maya to get tested and costs (there are some cheaper places in Cancun and Playa del Carmen): https://www.playadelcarmen.com/blog/covid-test-cancun-riviera-maya/
Not very well. The one place that we have found that has reasonable internet is a vegan restaurant called ArteSano, but the connection all over the island is not very good for video calls. Basic internet is available most places, but expect it to be very slow.
We will be setting up private transportation from Cancún airport to Chiquilá (where the ferries depart) for anyone interested. If you are planning on spending more time in the Riviera Maya, another option is to rent a car. If you do that, you can leave the car in one of the "estacionamientos" (parking lots) in Chiquilá for 100 pesos per day. We recommend "estacionamiento los delfines" on the main street going into Chiquilá. There are two ferry companies, each leaving every hour (one on the hour and one on the half hour). Updated schedules for one company (Holbox Express) can be found on their Facebook page: https://www.facebook.com/HolboxExpress/