Recommended charger for iPhone 5? I can see on the Apple store that the standard charger is a 12W charger.

Since it "should" output 5V, I can conclude it outputs 2.4A (12W/5V=2.4A).

Considering the above hypothesis correct, could any charger having the same output be used for my iPhone 5?
Yes, theoretically that's correct and there are thousands of chargers out there that will work with Apple products.  However, Apple includes specific components in their chargers to ensure their charging and communication protocols are followed.  They also have a licensing program for 3rd-party companies to manufacture and sell Apple-certified products, the MFI program. 

If you are looking for charging devices not manufactured by Apple but still follow the Apple-certification process, make sure the products display the MFI certication logo (not the 'Compatible with iPhone' logo which actually means nothing).