How do I effectively use offline documents on a WIFI-only tablet and other connected devices?
Try Autosync. There might be extra charges for syncing files larger than 8MB. https://play.google.com/store/apps/details?id=com.ttxapps.drivesync

Another option is FolderSync Lite (no file size limitations as far as I know):
https://play.google.com/store/apps/details?id=dk.tacit.android.foldersync.lite