You can have as many as you want as long as you have the bandwidth to feed them all. Nertflix has restrictions though. Six devices per account, including computers etc., is the limit. They also limit how many different programs you can stream a once depending on which subscription plan you have. One disc out at a time, one program, two disks, two programs three, three...
No, I don't work for Roku.
Netflix Player N1000X, XDS 2100X (premature death by lightning)
Roku2 XD 3050X, Roku2 XS 3100R, Roku2 4210R