A. Use NUS Downloader to download them on your pc then install with wad manager, or a version of dop-ios mod to download and install them directly on the wii.
B. Run Signcheck through HBC, press reset many times until it's finished, view the report on your computer. Or use the latest version of dop-ios mod which is in beta and run the syscheck feature.
C. You can install the patched system IOS for priiloader when you need to, even if it's already present on the system. Installing over current revisions overwrites it, just make sure the wad you're installing isn't corrupted and never uninstall any IOS under 200.
cIOS38Rev14 and 17 are currently considered the most stable revisions.