Ok, let's do some example case studies so I can better understand what's happening
1) I'm a nub who just learned about Homebrew and stuff, and I want to join in on the scene. However, I thought "loading stuff from an SD card" looked cool, so I updated to Wii Menu 4.0. Am I screwed from the time being?
2) I'm big on the Brawl+ scene, but I don't go into the other hacking things ("preloader? starfall? wtf are those?"). I'm already at Wii Menu 3.4, and I'm having no trouble with GeckoOS and Homebrew. What will I lose if I upgrade?
3) I'm a master hacker. I have the full package, everything short of hard-modding my Wii. I'm still at Wii Menu 3.2 because it's by far the best menu for my hacks. However, this 32 gb of storage looks pretty appealing, as my Wii is kinda tight on free space. Can I download drivers and IOSes that keep my stuff running, allow me to downgrade if I need to, and give me the Menu 3.2 experience with those little perks that 4.0 brings?