I have same scenario. WebDAV https via Synology DDNS with an auto-renewed Let’s Encrypt certificate.
I use Dropbox for the file repository for indexed files, and the WebDAV server for sync database, but I’m thinking to use the NAS for file repository as well via WebDAV from out of office.
(My 1019+ has a 1+1 TB of M.2 SDD as r/w cache and works reasonably fast).