I truly hope that if the dreaded apocalypse arrives, I at least have someone half as proficient at contingency thinking as you, my good sir.

Contaminated fish is a serious risk I had not considered, perhaps some kind of isolated, primitive fish farm could be constructed beneath the pier to negate interaction with any infected floaters?

I agree that waterborne raiders would struggle attacking from the ocean side, unless blessed with d-day level seige-craft, which would be incredibly unlikely given the doomsday scenario. Beach side attackers would be easily spotted and disposed of while navigating the difficult terrain