Can i turn my Old 2009 Imac into a Multi-use NAS server?
Sure you can.


Give that Mac a static IP on your home network.
Locate it near your home router so you can connect it to the router by Ethernet cable for stability and performance.
Set its power settings to never sleep.
Turn off or uninstall all unnecessary applications.
Think about what users/account settings you will use to allow access.
Set suitable ACL permissions on the directory you will use for the NAS root storage path.
Turn on AFP, SMB, or NFS sharing as needed.


You now have a basic NAS.