Visa and Mastercard are widely accepted. AMEX is less accepted in cheaper Latin American countries as their fees for the local businesses can be too expensive. Cash in the local currency is always the best option to pay.
The airport probably has the best exchange rate but you are able to exchange cash at the local banks as well. Bigger bills are preferred and they must be almost perfect to be exchanged at the banks, no rips, no crinkled cash, etc.
No, the outlets are the same as in the states. For my people outside of the US, yes, you will need your converters.
There are Ubers everywhere for under $10. Majority of the time, it costs between $3-$5 as the town is pretty compact. You may also rent ATVs or motorcycles to ride throughout the town for the day or week. We will have a list of prices via Simmon Tours and Rentals.
During the day, it can be from 70-80 degrees, and at night, it can drop to 50-60 degrees.