To the first question, the answer is yes: Processing allows to export a sketch to the form of an application for Windows, Linux or Mac.
To the second question, I would say "it depends"... You have at least three GUI libraries for Processing, it is indeed easy to code, but making graphical interfaces isn't the strong point of Processing, more aimed at low level graphics. Among other things, it depends on the complexity of the interface you plan to do.
Alternatives, like JavaFX or Pivot, can be worth a look, at least.

Great, thanks for the information and the alternatives.

I thing he's referring to apache's pivot

Ah, thank you.

Good catch, anchnk, I should have be more precise.
And I forgot to tell that the learning curve of these libraries can be higher than Processing's one, but it can pay at the end, as the interfaces can be richer. Depends if you want something more functional or more spectacular, though.