Re: walleye fly fishing.
For big flies I like the SA Pike/Musky taper line. I can put a pretty big fly far enough I won't spook 'em unless the fly does it.
I love the 15' two hander idea. As for single hand spey casting, experiment where on the line you should start at.
For Walleye I don't use sink tips. Or at least almost never. I get fish from really deep as well. It's a personal thing on how you want to do it, but I don't like Skagit or Scandi type stuff. I'v seem the Missouri by KC, is there some reason you ca't wade a few feet out? Your banks are a lot clearer than mine are and I don't need to get very far in the water.