I would suggest the MyCloud by Western Digital. Ethernet connected storage attached to WiFi router in sizes of one to 5 Terabites. Remanufactured devices further reduces the price. Any backup ap will find your storage device wherever you are. Alternative is any "Cloud" service that has free storage and only backup documents, pictures, and videos.
What is the most secure way to store files that must be accessed by various devices via our home network which includes both wired and wifi access. Access includes onsite and offsite locations. Operating Systems involved include Windows 10, macOS 10, Ubuntu 16, iOS 10, Android 6.