Welcome to the group.
I'm not sure you've received any responses to your questions.
For the fishing you are doing, you cannot go wrong with the Rio Outbound Short series of lines. A good thing and a bad thing there are a bunch of options.
For the surf, given that you need to go deeper, you can do the full sinking line. For deeper holes, this would work great. For the more shallow areas, you will be dragging along the bottom a lot. That might be ok, but the full intermediate might be better.
Both of those lines would work great from any watercraft.
Where you run into problems with the full intermediate or full sinking fly lines is fishing from the bank. I do most of my fishing on the potomac from Great Falls down to Fletchers. Between the bank/rocks and the deeper channels there are huge outcroppings of rocks/boulders that are sometimes visible, sometimes submerged. I have had a ton of success with the Rio Outbound Short multi-density lines. They float or sink very slowly out over the outcroppings, but then sink fast out further in the deeper channels.
The one I've highlighted might be the best compromise for bank fishing the Potomac, but the full sinking and full intermediate IMO are best for the other applications. And, Scientific Angler, BTW, has something similar. Personally, not sure why but I prefer the Rio lines slightly more.
Tom