The Office Suite is doing better than ever. I have no problem paying $129 a year for O365 with five users and each user can use it across Macs, Windows, iPhone, iPad and web. The iPad version with a Bluetooth keyboard and mouse is actually pretty good.
From your computer you attach a USB drive to your computer and move files like any other drive.
From an iPhone or iPad, you connect a USB drive to it using the USB C port, the USB drive shows up in the Files along with your OneDrive storage location and you move files to your drive.
The same way you would with GDrive, iCloud Drive or Dropbox
And 1TB of storage per user.