The RF Downstream specs for my Arris TM822G say it has a MoCA Immunity Filter. Does that mean I don't need to install a MoCA POE filter where the cable enters the house? I thought such a filter ...

As a standard practice, major cable providers install point-of entry (POE) filters before activating your internet service. The filter isolates the MoCA signal, keeping it out of your neighbor’s ...

You should only need one POE filter, at the main line. Possibly one in front of the cable modem if you're worried about interference there, but newer modems have it built in.