#1
Kirk Hammett said he used 3 wah pedals in a song from their last album. I wish he would tone that shit down. How many wah solos has he done? 
#2
too many
There's no such thing; there never was. Where I am going you cannot follow me now.
#3
3 wah pedals seems excessive, unless one craps out regularly. At that point why would you keep it in the chain?
Guitar/Bass:
Schecter: Damien 6/Stilletto Extreme 5, Squier: Bullet HSS*, Washburn RX10*/WG-587, Agile Septor 727
*mods

Amps/FX
Peavey: Vypyr 30/Max 112 (200W), ISP: Decimator

Quote by dannyalcatraz
Understood- I waste money on amps*, too.

justinguitar.com is the answer
#4
The only reason you would use 3 wah pedals is if you are making some weird-ass noise/sound effect, and given the nature of Metallica's music I doubt that is the case. Unless he means he played three solos in this particular song, and used a different wah pedal on each one.

To answer your question, pretty much all of Kirk's solos feature wah.