Here's my 2 cents worth....
The gap in the first picture of post #464 really needs to have some plants there to add some green, color, and to soften up your fabulous deck.
You can Google plants that tolerate salt spray for lots of suggestions. The one I liked is the flower carpet rose, but there are many others. You may not need to worry about splash out in that area. If not, I love my new drift roses. So far since July 24th, they've been in constant bloom. I always feel like something blooming most of the year is a no brainer.
Now for watering the bed... I would have the irrigation (or whomever will be doing your sprinklers) connect a drip line from the closest sprinkler pvc. It's a small black tube which would be easily hidden by tacking or gluing it along the step bottom.
My landscapers added 5 different spots with drip lines for my deck. It was cheap and easy for them to do. I love it! I should have done that years ago. So now, my potted plants get the water they need without relying on me to water them.
It doesn't matter that yours aren't in pots. A drip line would work for your issue of accessibility.
Suz.