SMS relay requires just any network connection. Does not use Bluetooth.
WiFi calls require the devices to be on the same network (doesn't have to be same WiFi AP even, as long as they're both connected to the same network). Also doesn't use Bluetooth.
Only the Handoff and Instant Hospot features use Bluetooth, so you have to be within 20-50 ft or so. Depends on the environment, walls, building construction, etc.
My apartment isn't that big, so I only know Handoff works from about 20ft away through a wall