A:AnswerYes it is compatible infinity modem, & very easy setup. I would recommend this extender to anyone, I would buy it again if need additional extenders.
A:AnswerYes, you may use multiple extenders in an environment, just make sure that you use the main network name and password, so as to not confuse users.
A:AnswerNot sure. I place mine about 40 feet from the router and it extends the signal about 40 more feet to my back yard. OK for using my phone but do not use with Roku.