Doing whatever you want on your emunand while keeping it offline from nintendo and then booting into a clean sysnand to play online isn't a ban so far. Just don't connect to nintendo on your emunand and only connect to nintendo on your sysnand if it's clean and you're good.
1) You would update the clean sysnand through nintendo servers and this would remove autorcm and burn fuses on the reboot. If you have an unpatched console you can downgrade even with burned fuses (you probably don't want to downgrade anyway) I boot my sysnand by turning my console on normally...
When you actually install the game it will be the same size as if you just installed the nsp.
the benefits of NSZ are that it's easier to download and store since the file size is smaller and it will install quicker.
NSZ is the same as NSP only smaller
NSP's contain NCA's whereas NSZ's contain NCZ's
NCZ's are compressed NCA's
so yeah they're basically the exact same shit just smaller.
Format your 256gb card to FAT32 (use a tool such as guiformat) since exFAT formatted cards are known to corrupt. The switch always supports FAT32 So you won't need to do an update.
If you want to update your sysnand then it's safe to do so through Nintendo servers assuming it's clean. To update...