Installing Nominatim on a server

Hi guys, I’m a noobie here and I want to install Nominatim only for reverse geocoding on my server. my case is, for example, I want to import only Iran to my database but I want to have the names of the states and cities when I do a reverse geocode lookup. I don’t want to download the whole world. Can anyone help me to get started, and for example for Iran and it’s states how much storage I need. and how can I find out how much storage I need for the X country if I want to download the country for reverse geocoding?