A stainless bolt and nut, with a washers too, will work fine. Use some bolt anti-seize on your new ones! The original had a nut also. My recommendation is, if you are fortunate to have a Marsh Fasteners store near enough, go for 316 stainless, which is a better corrosion resistance than even 304. If that isn't possible do make sure that the "stainless" hardware you get is really that. I have had some uneven success with stuff from the hardware stores. Some is totally fine, but some didn't do well at all. Bring a magnet to test
!
For paint, there are various opinions of course. I have grown to really like Krylon's newer High Heat Max. It seems to me to dry much faster and be less prone to runs. I personally like their kind of semi-gloss type for all of the black (sides and firebox), but others prefer using a flat or at least satin black on the actual firebox. If I ever do a classic redhead I will actually do that myself. But for Silvers and other newer grills, I just personally prefer using the richer black on both. Just my own preference. It's what makes the world go around.
Here is a crazy Sunbeam restore where I used the semi-gloss black on the top and bottom. I am sure the original was all flat black, but I think this color made it look classier:
Here is an unrestored Genesis 1x00. You can still see that the side caps were a semi-gloss but that the bottom firebox was a flat black:
Also, Rustoleum makes an excellent high heat paint as well.