Update your sysCheck with the latest version from
https://gbatemp.net/threads/posting-a-system-check.300279/ and follow the instructions there for posting a syscheck. It also tells you how to ignore a particular problem IOS.
This "special ModMii" screen you keep mentioning is probably from a custom system menu theme. In which case, it will be gone once you update the console. But don't update it yet, that should be the final step after you've removed everything else, to restore the stubbed IOSes that cIOS overwrites.
Building a new NAND is not necessary, but it is the only way to remove absolutely all traces of a previously hacked console. But an average end user can not spot those traces, they're only relevant for warranty, and all Wiis have been out of warranty for a long time now, so they really don't matter. It's much easier to simply delete any cIOSes, uninstall Priiloader, BootMii, uninstall any homebrew related channels and pirated VC/WiiWare and then updating the console. Building a new NAND is usually reserved for problem Wiis which exhibit strange issues that can't be fixed any other way.