€ Euros. ATMs and small currency exchangers generally offer better rates than the banks. Some smaller restaurants and cafes may not accept credit cards so look for signs or ask to be sure before you order.
Portuguese. English and Spanish are also very widely spoken in Faro, as well as some French and German.
+351 for Portugal followed by 289 for Faro.
The local mosquito population can be rather fierce, particularly by fresh water so make sure to take some mosquito repellent!
As part of the EU, all you need to enter Portugal is a valid passport, which entitles you to stay for up to 3 months. After this time you'll need to register yourself as a resident with the local authorities.