This is correct, Wii is perfectly fine to use, everyone uses Wii for runs. Also yes, its GC on site because the game came out for the GC.
any means of speedrunning Prime are allowed above each categories respective video cutoff time, so yes. for any% the cutoff is 1:10 IGT and for 100% its 1:30 IGT. 21% requires video for any completion. Once you pass the video requirement you will need original hardware and a disc.
I will agree Glitchless is "less arbitrary" partly due to it actually being a full game run, but the biggest reason I won't advocate it to be a main category is unlike many other games where the definition of a glitch is clear, in Prime its very hard to determine what is a glitch and what isn't. This can also be applied to your idea of no major skips. Due to this gray area of being unable to accurately define a glitch in this game I think its fitting on this LB, but as I stated before, I will try to make this LB more known to the general public. Also i'm not saying it won't ever happen, if it grew somehow and got lots of people wanting to run it (And a clear definition of glitchless made) then it could make its way to the main LB, but that is not happening anytime soon. We didn't spend very long deciding the ruleset for glitchless (It was roughly a 1-2 hour discord call) but even in that time there was lots of arguing over whats actually a glitch, and what isn't. Most notable is whether or not R Jumping should be allowed, which I allowed in the end. Regarding moderation, due to Prime being a relatively inactive game I think both this LB and the main LB are stocked up on mods currently. I appreciate the offer though.
The reason glitchless is not on the main LB is because it is not a main category, it's very arbitrary and can't properly be enforced in any sensible way. Personally I will not watch an entire run just to make sure nobody breaks the very specific ruleset. I stand by DCR about the decision for this LB. Perhaps it could be mentioned in more places so people know these extension categories exist and I will try to find a way to do so.
Version differences could be all on the same leaderboard but have an easy identification as to not make many categories
Interesting ideas but I have to ask why? Nobody runs any version but 0-00 and it will only be ever ran as a joke.
Gamecube and Wii seperation makes sense but really isn't necessary imo, just adds more hassle all around
Segmented would be a nice addition, might push people to do it more