If the fans are the same voltage as the extruder heaters, you can use a common positive wire for both extruder heaters and both fans, but make sure it can carry the combined current - in particular the full current draw of both heaters.
If you have an endstop switch on the X carriage, and it's a simple 2-wire microswitch or it is using 3.3V power (not 5V or greater) then the Z probe and the endstop switch can share the ground wire, and the +3.3V wire if the endstop switch needs it.
The two thermistors can share the VSSA wire.
For the next generation Duet, we may make a hot end board that would need just a 2-pin power connector and an RJ11 connection.