YES! Tests can be arranged by the front desk of your hotel or you can easily visit any of the mobile testing sites all along the main beach road. We've found many testing sites readily available on our last visit to Tulum. These cost $35-50 and you'll get your results within an hour.
We've found that all hotels and restaurants have WiFi in Tulum Beach, so you can stay connected wherever you go. WhatsApp is widely used in Mexico and we highly recommend it. Hotels and restaurants commonly use it for reservations or questions and it's incredibly easy to communicate via text this way.
Friday night attire - think "Going out to a nice dinner on a beach vacation" Wedding night attire - Beach formal- jackets optional, no shorts please
Most places will happily take USD, and we advise on bringing cash with you for sure. That being said, we recommend exchanging some cash for pesos if possible. You can do this either at the Cancun airport, or any of the banks in town. There are also some currency exchange centers and ATMs along Tulum Beach, but the open hours are variable.
Yes, Tulum is safe. The people are incredibly nice. However, being in another country requires that you respect a culture different from your own and you'll probably have to behave a little better than you would at home. What I'm trying to say is, don't be a drunk a-hole and wander off alone in the middle of the night. That isn't smart anywhere you go.