If your number of gateway points are low, using something like syncthing for the glue between the nodes is a perfectly acceptable, mesh, way to do things. As well, this can be directed to only operate without DHT and only over VPN tunnels to deal with the in-flight tunnel encryption. As for each location’s redundancy, that’s dealers choice… ZFS is always a good option if you set it up right and you grow in predictable and repeatable chunks, but things like Ceph work more on the scalable side if you know you’ll be growing frequently and at varied rates. Either way- you grow each node the same as each has a copy.
All of that “works” out of the box as well.