I have purchased fog lights similar to the original ones offered by Ford from CJ Pony, along with the switch that goes on the center console, and the relay.
I get really confused on the best way to wire these though - some state you really need the $89.00 wiring harness, others seem to mention wiring into the fuse block, etc -

What is the best way to do this? Is the wiring harness worth it? Is the wiring harness easy to replace?

I was also wondering for foggy driving if it is worth it to have the fog lights wired so you don't have to have the low beams on, or do they hamper foggy driving?

I was reading nightmare posts about the foglights and the computer controlled stuff on this site on the 2004 or so Mustangs -

 

Your car should already have the foglight wiring installed. Just plug the switch into the factory harness tap into a power wire and run the wire to the fogs.