I played around with the nylon cone versions. I think they would work better than the spring versions. I don't think the nylon will interfere with electrical ground. The metal part of the nut is against the rails, and is also what the screws thread into. The panels are also going to be sitting on the rails. Our local box store didn't have enough of them, and since I used the same ones for the roof, buying a 100 piece box saved some bucks...
Apparently galvanized metal is less conductive than ungalvanized. but my guess is it should work.
1/2" is going to be way to be big, though. Your panels are calling for an M8 bolt in one of the figures, and M6 in other? That's odd... I don't think your going to find metric sized cone nuts, at least not locally. 5/16" would be the closest imperial match to M8, 5/16" = .316, and the M8 = 3.150. The hole in the panels is 9mm wide, which is 3.54, so you should be fine those. Or go with 1/4" which is .25", of course, and M6 is .236. Worth trying a couple of options before you buy a bunch of them, maybe.
The panel frames are aluminum. I'm used to fiddling with things on sailboats where we don't like to mix aluminum with stainless or galvanized without some sort of isolation, or we're in a world of hurt with galvanic corrosion. I think it's much more of an issue with salt water. My boat is in fresh, and I see it a little, but not near as much. Unless you're dealing with extremely high humidity you should be fine.
The caveat with dissimilar metals is checking whatever bolts you use actually thread into the nuts. When I tried the box store versions of galvanized bolts, they would not thread into the channel nuts they had even though they were the same size and thread pitch. I think the nuts were ungalvanized zinc (not a great choice for outside anyway)...