1) I'm not sure about the 78-stage one, but I've uploaded a modlauncher for riivo that allows for around 30 or so.
2) You're right about that, at least from my experience.
3) You probably know that Riivo can play alternate cutscenes. Riivo is also a lot quicker to launch, since it only loads the files you need instead of every single one all at once.
Hope that helps!
With that xml, how do you have to have files arranged? I've been using the Ocarina xml and I have, in my RSBE folder, BalancedBrawl; BrawlMinus; BrawlPlus; and shared.
Basically everything is in my shared folder, since I don't care about Minus Balanced or whatever and is organized like the standard way.
I tried following the directions using the standard format and I get the different stage menu with a ton of hanebow stages on the second page. I put in the st_customXX.rel and st_customXX.pac in the right folder and numbered the right location (i don't mess up with .rel related matters).
When I chose the stage, the game stopped running, but the home button on the wiimote still worked with all its functions.