WiFi HDD with OWRTfirmware: how to NAS and join home network

I have an HDD in WiFi box, that has only USB and WiFi (no ethernet at all). The stock fw was owful and there was a guy who tuned Owrt to be used with it [https://forum.openwrt.org/viewtopic.php?id=72247]
I need help and hints to understand, if it is possible to tune owrt into NAS. The stock fw was used to make an access point and share HDD connected connect any device to this NAS (like: use files if necessary; disconnect and connect to a (home)network to have internet and printers). But I would like to have this device connected to my home wifi network and HDD shared over it.

Any advice and links to proper mans would be gratefully awaited.I have very moderate linux experience, but would like to make the device work as described.