For archival properties, it seems that gold toner (the one with real metal gold, not the coloring ones that make it look gold-ish) is the only real game in town, i.e. the one on which the experts don't disagree.
With selenium, it seems there's a lot of controversy regarding archival properties; personally I don't care, and I use it rather to change the tone of FB prints.
Most FB paper have an olive-green cast (that I actually never noticed until I toned my prints...) that selenium will help neutralize. I dilute 1+19 KRST to work slowly and get the print where I want it to be. For a paper that tones well, I get a fairly neutral tone around 4-5 mins. If I go for full toning (8-10 mins), then I have a pleasing eggplant/brown tone that goes lovely with certain pictures.
Of course once you know what kind of tone you like, you can augment the dilution to work faster, but you may end up waste more toner if you don't do it enough.
Regarding safety, with selenium it's important that you have some good ventilation (an open window, a door). Buying nitrile gloves from the drugstore could be a good idea as well to protect your hands. It's not nitric acid, so you won't die if a drop falls on your hand, but you don't want to ingest some by accident from not washing your hands.
I could never get any tone change from an Ilford MGIV FB paper. More traditional (old-tech) brands like Foma, Forte, and by extension most of the Arista line, Bergger, are much more responsive to toning.