I had many of the same questions before I started fishing in Gaspe several years ago. The answer you get to most of these questions can change depending on who you talk to (especially about things like brass tubes).
To be honest, in all of the rivers I've fished there (York, Dartmouth, St. Jean, Petite Casc., Bonny, Nouvelle) I've never actually needed anything other than a floating line and flies tied on single or double salmon irons. I did get a couple of grilse using plastic tubes with the tippet coming through the side (sort of the equivalent of hitching a traditional fly). In typical fall conditions, the water will be clear and not too high, and the salmon certainly see the fly. I've had fish rocket off the bottom in very deep pools to grab very small flies fished from floating line in Sept. This year, the water might be higher than normal for fall, but probably not higher than early June. Even then, I use only floating lines with great success.
I have seen several anglers fishing with sink tips and even full sink (!) lines during very low flows in Sept in years past. They drag big flies through pools stacked with fish, and certainly their aim is to snag or at least floss fish. Definitely not sporting.