Don't forget to grease the threads, and to use flat and lockwashers where appropriate. Torque them firmly; a properly-torqued fastener should not need Loctite or similar to stay put. Any fender stays should be mounted outboard of the rack stays to minimize bending stress on the fasteners. Don't skimp on the fastener length; screws can be easily shortened for a just-right fit. Ideally at least one full thread should protrude from the nut/eyelet.

I suggest stainless (technically, corrosion resistant) hardware for its, well, corrosion resistance. And hex socket cap screws are superior to hex or Phillips head screws for this application, IMO.