NetGroup.receiveMode only affects how directed routing (NetGroup.sendToNearest()) behaves. it doesn't affect group topology in any way, so it has no effect on the scalability of the group.
if you want to override multicast stream parameters like multicastPushNeighborLimit and multicastWindowDuration at a receiver, you must set them to your override values each time you get a NetStream.MulticastStream.Reset NetStatusEvent. otherwise your local changes may be overwritten by new low-level multicast streams as your node latches onto one or the another as they are flowing through the group (note that multiple publishers can publish the same named stream in the same group; receivers saying ns.play(thatName) will get one of them, and may hunt and re-latch if one stream goes idle or inactive). each time the NetStream latches onto a new low-level multicast stream you'll get a NetStream.MulticastStream.Reset event, so you know you need to re-apply your local overrides.
if all you are doing is multicast, then the properties of a NetGroup.info will all be 0 because those properties measure the performance of all the group modes *except* for multicast. multicast-related/specific stats are accessed via NetStream.multicastInfo.
group peers don't appear in NetStream.peerStreams. that's only for 1-1 direct connection NetStreams.
Thanks for your patient reply. Thanks very much.