No, you don't need an internet connection. The Forscan software requires certain versions of the ELM327 chip (its on their website), but I can't speak to the compatibility with other software. The link I sent is for the tool I own, maybe you need to scroll down past the other tools to become visible.
The tool will work with all OBD2 ports, but Forscan is for Ford, Lincoln, Mercury, and Mazda. I have some software that accesses all makes, though the company is now defunct. A little research will yield a vast selection of software, so just do a little research.
Comparing Forscan with my other software: the free version of Forscan is vastly more detailed, it even has the ability to program PATS keys, though you need to purchase a license for that feature (I've never needed to program keys).