So I've recently interviewed for a job that would involve guiding teens on backpacking trips on the Northern Washington Coast. This would mean two-week, low-mileage trips in very wet and sometimes windy conditions with temperatures probably varying from 40F-60F most of the time. My personal gear is fairly light but my pack weight will be increased by things like sat phone, bear canisters, big first aid kit, etc. Sometimes I would have to take weight off of participants so it is possible that at times I would carry more than 65lb. Some of the hiking is on beaches, other on trails that are sometimes very muddy and sometimes very rocky and probably steep in spots going over headlands. Daily mileage is supposed to be small, say 3-5 miles a day.
I'm considering what sort of shoes would work best. I have a pretty fair number of options. Mounaineering boots, some mid-weight hikers that don't fit all that well, regular running shoes, some minimalist trail-runners that I picked up used, and Chaco Z-1 sandals.
The company recommends mid-weight leather boots of course. I'm suspecting that the salt will wreck the leather and that my feet would stay healthier if I let them breath and drain more.
I used to have a tendency to twist my ankles a lot before I developed a mountaineering boot and trekking pole habit. I do have small, weak ankles. I've since concluded that the poles can let me use less-supportive footwear. I still wear boots a lot because I want them for mountaineering, although a lot of mild approaches I've taken to doing in running shoes.
My first inclination is to take the Chaco sandals, as I think they would stand up to the salt and sand well. I've considered taking neoprene socks for colder weather and some fuzzy wool socks for around camp. Does anyone have experience with this sort of system for beach-and-mud hiking? Can anyone comment from experience about carrying a very heavy pack with sandals?
I've read about all-synthetic trail runners not standing up to abrasion well. Are there any good reports for shoes that have excellent traction and put up with salt, sand, mud, rocks and brush well?
I have a narrow, high-arched foot that tends to over-pronate if that is relevant.
Thanks in advance for all input.

