I've found the answer to the first question here, it is possible to connect the Era 100 speakers as surrounds.
Though some reported problems with the latest S2 app update and you might find it difficult to connect the speakers or remove them from the surround setup.
I'm also interested if the setup is equivalent to a 7.1 or 5.1 (my guess it is the former) as I am about to make the same purchase as you.
A Beam Gen 1 would be 5.0 - Left/Center/Right Fronts, Left/Right Surround ( +.1 if you have a Sub). But nowadays, don’t get all hung up on number of channels (and never think more channels are automatically “better”. We are quickly moving toward a spatial audio concept, where the place in the room the sound is supposed to be determines which channel/speaker it is played on. So depending on the room and speakers placement, the “channel” used in my setup to play a sound will be completely different from the “channel” in another room/setup.