Lifelines

[Brion Toss]

Hello,
And welcome back! Yes, type 316, 1x19 would be the best choice for wire, because that alloy is most corrosion-resistant of the types generally available, and because that construction presents the highest ratio of volume to surface area, thus the least vulnerability to surface corrosion.
Rotaries are the best swages, but if you use them, get the swager to dip the ends in Boatlife or the like before swaging, to prevent internal corrosion.
And maybe you might reconsider high-modulus rope lifelines. They don't corrode or fatigue, are easy to splice, and can last as long as wire ones, given adequate UV coating and diameter. Softer to land on, too.
Fair leads,
Brion Toss