Computer A is your server. You don't need more than 1 module (to actiavte MP - which require a license, hence you cannot use DCS World Free for this).
Computer A use 1 serial which you have to buy. You can't use this serial anywhere else.
You decide which module you want to buy for this server.
Computer B, install all the modules - and make sure you have 1 unique serial for each.
Computer A isn't locking any aircraft/slots. It only locks down 1 serial.
When you log in to MP, that serial is marked as "in use" and can't be used on another PC (until you log out).