What clips to use in a Marine Environment?

I am doing a remodel project in northern Washington State (San Juan Islands). Plenty of Marine air in this area and the cabin is on a cliff above a beach. PLENTY of wind & rain in the winter too. We are considering a metal roof. Nobody around here has done aluminum, so steel seems to be the only choice. I have numerous questions. The roof is a 3.5 / 12 Hip Roof, with a small cricket to the chimney. There is a carport attached with a 1 (maybe .5) / 12 pitch. There are two pipe vents, one stovetop fan vent, a bath fan vent and 5 roof jack vents presently. 1. ) Can someone please explain how vent pipes and fan jacks/vents are properly covered or installed? I have seen some pretty sloppy jobs on YouTube. I want them done properly, so they never leak and so they look good, as the cabin is very low to the ground and the roof is really prominent. 2.) Should I spec out SS clips & screws? Is this necessary even though they are covered with roofing? 3.) Should the carport's present torch down be removed and the existing 2x6 Car Decking be covered with 1/2" or 5/8" plywood and ice & water shield? 4.) If the roofers must use sealant anywhere, what is the best bullet proof sealant for them to use? (Can these roofs ever be done without sealant?) This cabin has been passed down in our family since the 1800's so it's not the typical roof that will be sold in 7 years. Longevity is a big goal on this project. BTW, I want the seam to be double mechanically seamed too. Nu-Ray Metals is big in this area and they have a panel (NRM-2000 Mechanically-seamed panel ideal for low slope roofs; 1½? rib height) that seems to meet my purpose. Your thoughts & suggestions are appreciated! Thanks very much.

1. Depends on where the pipe boot falls but Dektite makes plenty of options and you can cover the exposed boot with a plastic cover to protect it from UV. 2. We usually run SS clips but a type of climasealed screw with a plasticized coating on it. 3. I would do it all in metal if you should remove it and put a new deck down. 4. Depends on if they are color matching but Geocel makes a good sealant I can't believe that in a coastal environment that nobody is running aluminum coil?