It is difficult to get around with a paper map unless you are sticking entirely to main routes. Google maps app is pretty good, much better than a Garmin, except in mountainous areas where there is no data. In the mountains, it is better to have satellite. For cell, it is better to have a service that is sold in Puerto Rico. At Sitka mentioned, ATT has great coverage. If you have Verizon, expect problems with data. We switched to ATT prior to buying our house because the coverage is so much better.
As far as getting around, do the same things you would in the States. Stay out of bad areas in cities. If you have questions, ask your hotel. Locals generally are very kind and helpful. Many people, especially the younger people, speak English.
Also, check out They have some great suggestions and provide GPS coordinates for many places.
Hope this helps.