The Beam is a soundbar (FL-Center-FR) so there’s no need for front speakers in a Sonos surround set up. In fact, the app won’t let you ad speakers other than as surround rears.

You also can’t set up four speakers in the same “room” in the app - two is max. And how would you connect them to your TV?

By the way, the speakers are called One SL. Sonos stopped using the “Play” in their naming some time ago. One SL are the direct successor of your Play 1’s and they’re not very much different soundwise. 

For music sources you could add all the speakers you want to a room in your house but a Sonos Room (which is different) can only have one speaker, a Pair of speakers or a surround system.

To make it worse you can have multiple Sonos Rooms in each room of your house.

I’m listening in my computer room right now, to a Sonos Room called Computer with a 5.1 Beam setup and a single One SL in a Sonos Room called Computer 2.

Made more sense before the marketing types made them quit saying Zone instead of Sonos Room.