For goats I'd say about 1.5 metres apart, their buggers for standing on the wire and it sags after a while. I've put a rail on the top of my fencing so they tend to rest their front feet on it (rather than the wire) while forraging in the hedge, and I've also stapled the wire to the back of the rail.
As already said, 4inch round posts with 6 inch strainers