SPB ISIS adjacencies are point-point only. If doing Fabric Connect SPB over a WAN, you will need to use Fabric Extend. There are 2 Fabric Extend modes, using VXLAN and using VLAN translation (of the BVIDs). In your case it sounds like the operator is giving you a VPLS (L2 any-any) service. You will thus need to use the Fabric Extend VXLAN mode (to male it look like point-point to SPB). In this mode, you set the FE source IP on the VSP, and then created FE ISIS adjacency towards remote IP addresses using logical ISIS interfaces. A VXLAN tunnel is used for each of those remote adjacencies. And yes, you can now have all your logical ISIS adjacencies running on the same physical Ethernet port.