I have 3 mac minis. should i use a different icloud address for each mini.

Not sure what you mean by using a different iCloud address. If you mean a different Apple ID/Account then that won't change how you see them on your home network and it will mean you can't synch calendars, files, etc. between them. It really depends on what you do with them.

If you want to differentiate them on your home network then just give them different names in

System Settings/General/About

iCloud is a synchronization service. It's used in the background if you want to synch calendar, notes, reminders between your Macs and also with any iPads, iPhones. It can also synch files and pictures (via the Photos app). You don't have to use icloud if you're not bothered about keeping those things in synch across your devices but if you do they all need to be signed in to the same iCloud account.

If all your Macs are on your home network and not mobile then you don't need iCloud for sharing files.

If you decide to use iCloud for photos then read up on it first because it could have implications on how much space you need. I don't use it so can't help.

All this depends on your use-case, obviously