I've been floating in Bristol Bay and more recently, the Y-K delta, every other year since 98, and the absolute most miserable I've seen someone was a guy on the 06 trip wearing the rubberized HH commercial fishing gear on a trip where it rained solid 7 out of 8 days. It for sure keeps rain on the outside, but the guy who wore it was wetter from the condensation inside than everyone else was from the rain. If you were just fishing from a boat with someone else rowing and such, it would probably be fine.
The statement you've heard - "buy the best you can afford" is, verbatim, the first line of a lengthy list of things that we send 'new guys' on our trips. It's followed closely by "don't bring any cotton on the river". You can replace the term 'Gore-Tex' with 'Waterproof/Breathable' since a lot of companies are making their own version that is (generally speaking) the same stuff and just as good as the companies licensing it directly from WL Gore. All of the WP/breathable stuff will lose effectiveness over time or as it becomes saturated.
The most common place guys get wet is up the arms from handling fish, etc and water then wicking all the way up the arms. A lot of the fishing-focused jackets now have very solid seam closures and rubberized cuffs to prevent this, whereas most of the hunting jackets don't. Not sure about Kuiu.
Wading length vs Full length depends on the conditions you think you'll face. If it's early kings or late silvers, you'll be wading deeper than normal and a wading cut jacket makes sense otherwise a good portion of the bottom of the jacket is going to be in the water. If it's mid-season trout fishing or mostly fishing from a boat, the full length is a little more versatile, since full-length makes more sense in most other (non wading) situations. Unless you plan to use it almost exclusively for fishing, I'd buy full length.
I'd frankly be more nervous about rental waders and boots. Even the highest of the high end lodges won't necessarily catch every pinhole leak, seam rupture, etc. in their gear as the season rolls along.