As to the original question -- I'm far from a master at big water trolling, but what I do know is... it doesn't matter that much.
Use braid (which I don't like as much, because if you do get a tangle, it takes too long to fix), use 25# mono, use 60# mono... it will all work, and I've seen it all work. My personal trolling rod (I don't have a boat, but most of my fishing buddies do) is 30# mono with 25# leader, which I'll use for everything -- trolling the bay, backtrolling plugs in the tribs in winter, anchor-rotting on the Columbia... it works just fine.
For what you're doing, just use a leader lighter than the mainline (big water nooks will hit it with a winch cable on it), use a quality bead chain(fancy swivel) at the end of the mainline, and use lighter dropper than leader, and you'll be fine. I don't use a spreader, I put a small corky at the end of my mainline above the bead chain, and I tie the dropper/weight to a snap swivel (or just a snap, whatever's in the tackle box) (both ends) and clip it on the mainline above the corky (corky keeps it from hanging up on the swivel). Easy to change weights, and being a slider, is more sensitive.
But really, not one setup described in this thread is "wrong." Whole buncha ways to do it, figure out your favorite, since they all work.