That works. It all depends on your trellising system. My cascades are growing up aircraft cable running up a pole. I allow 4 - 5 bines per line.
Regarding the arbor that the OP showed us. I would do like 2 on each side. Once they are established next year those hops are going to be sending up dozens of little shoots all season. If you let too many grow it will get tight. And of course, that invites disease.