Updating from nintendo probably won't brick it. Still, there's not much progress between the firmwares. Or even none at all above 4.1.
Modmii, as suggested by psincd, is like a swiss army knife for modding. It can do pretty much anything, so I'll focus on what it is that you should be doing:
1) use an exploit to reinstall the homebrew channel and bootmii (probably bannerbomb, but I'm not sure on the version).
2) if you don't have a bootmii backup, make one now
3) update your IOS, cIOS and/or channels with modmii. If you want to update the system menu as well, that's fine too...as long as you make sure you have the corresponding non-stubbed IOS to go with it.
4) install priiloader and block disc & online updates
5) get the loader of your liking and install it
6) your USB drive...get it formatted in FAT32 (WBFS is outdated). Then use a program like wii backup manager to move your games over there.
That's, roughly said, what following the modmii tutorial will get you: a wii with the latest cIOS and, generally speaking, the most safe way to get there.
Important: there are no prerequisites. Just treat your wii as if it wasn't modded before.