syncthing takes a lot of time building up its indexes
for 720 GB it takes on my ODROID ARM machines around ten hours on luks-encrypted volumes
setting up a new server i start syncthing with no shared dirs
if it is running (webinterface shows up) then I add a folder
after this folder is synced as it should I add the other folders and let the server work...
This might be easier if you already have some other machines syncing happily:
Make sure (on the new server) that the prefix for folders is the right one and add your new server to another already working one and then enable sharing there. Then just hit "OK" when asked if to share on your new server.