Yeah, specs say 4 SAS ports only through the external connector and 4 internal SATA ports. The external SAS port can be used for SAS or SATA, the internal SATA ports are SATA only.
The external connector assumes you’re using external enclosures. If you want to you can loop it back inside the case but it’ll require the case to have up to 8 SATA power connectors which is slightly unusual (assuming you’re using the internal SATA connectors as well).
Wireless backhaul works fine if you put the extenders in place before the WiFi turns to trash (roughly neg 60-70db).
Pretty much everything plugged into the outlets bothers Powerline. Refrigerators, microwaves, ovens are probably the worst. Even using outlets on different breakers bothers it.