If you'll just be around San Juan, my main recommendation is to be careful for thiefs. There is alot of criminality in that area.
There are alot of 2Gs around here, not many 1Gs, but most of them do not even know what DSM means. [At least the ones I know of]
In that area, alot of people street race. Cops try to be strict, but our goverment is a bit corrupted. Many cops building false cases, taking advantage of people, etc.
I do not mean to scare you, its a great island.
Emission laws only harm you when you go to get your car inspected. If it fails to pass the inspection, you give the inspector 20 dollars, and you miraculously pass it.
You have to get your car inspected once a year.
Have fun!