And looking at the device you're using... I don't think it's suitable for a NAS setup, but you could get a Mac Mini and connect that to it, and then use file sharing on that to have it act as a NAS.
This was my earlier thought but I didn't really want to have an extra computer using electricity all day long (save the planet/startup etc - the mini probably uses less power than my phone but in my head etc...)
And looking at the device you're using... I don't think it's suitable for a NAS setup, but you could get a Mac Mini and connect that to it, and then use file sharing on that to have it act as a NAS.