Just managed to move most of our stuff from an internal SATA drive to an external eSATA, thereby moving it from the firewall/fileserver here in the house to the SunRay terminalserver.
Worked perfectly, and actually… made life a little easier for the end users (a.k.a. “the family”).
What remains is to move the firewall/dhcp service from an Intel Atom 330 to an (ancient) VIA Epia machine booting of a CF-card and running pfSense. It should easily handle the firewall duties, but in case the dhcp needed for the SunRay terminals is out of bounds, that shall be moved to the SunRay server itself.