I have all Canon image adjustments turned off, long exposure noise reduction, high ISO noise reduction etc etc, and fix in post.
Long exposure noise reduction is dark frame subtraction
https://www.google.com.au/search?safe=off&client=firefox-a&hs=6mB&rls=org.mozilla:en-US:official&q=dark+frame+subtraction&spell=1&sa=X&ei=sXWJUePqJ4KEiAeE1YCAAQ&ved=0CC8QvwUoAA&biw=1920&bih=1001Same thing, one is done in camera and means you miss half your shots, the other is done in post and means you capture as much as possible.
With camera on tripod you want lowest possible true ISO for least noise and longer shutter speeds (so your not replacing the shutter every other month)
You now have 2 exposures to deal with. 1 for the lightning and 1 for the ambient. Aperture will control how bright your lightning (think of it as a speedlight) exposure is (how bright each strike is), and shutter will control how bright your ambient (everything else) is.
f/8.0 or so should be a good start for the lightning. Try and capture some and check it's exposure. It's pretty easy to dial back the blow-out on lightning in post, so don't worry if it's getting blown out heaps. And if you are capturing ambient surrounding, you want to stay under your cameras 'diffraction limited aperture'.
Now take a test exposure for ambient. Try 30 secs. If the ambient is to bright use a shorter shutter speed.
Enable intervalometer in ML, hit start, have coffee and enjoy the show.
Seems like it could get multiple strikes at once where motion detect will not.
You'll get as many strikes as you can. If it's an active storm front, you could end up with 5 or more strikes in one frame without any post blending.