You have a lot of good ideas here on how to clean and protect the fiberglass surfaces of your baby, but the best thing is to make sure you always have a good wax coating and to keep the sun off as much as possible. This will help keep the resin and gellcoat from chalking.
Also, if you ever have any divers do some any artifact recovery, try to keep them out of the boat on a swim platform. If you have to have them in side of the transom, then put them into a bucket.
Iron is real bad as there will be both Ferric Oxide (Iron III - Fe2O3) or red rust and Ferrous Oxide (Iron II - FeO) or Black Iron or Black Rust. You can clean Ferric Oxide fairly easily but will be scrubbing at Ferrous Oxide for a long time. If it gets into the non-slip areas you may have no choice but to compound it out. Ferrous Oxide is used as a black pigment and is in many inks, so just keep it out of the boat.