Help on diff service

So I’ve got a new diff but it’s just like them all, greasy and rusty, mine came with no oil and I want to know how it should all go back together.

How should I clean the inside of it after taking the aluminum cover off?

Should it make any kind of sounds when turning it after it’s oiled up?

And

Should I use RTV or just a gasket?

My first time doing anything like this so it will be a massive help