Most people recommend adding the Sub first because the added bass gives you a more cinematic experience. But if you prefer more of a surround experience over more bass, go with the Play:1s or One SLs.

Play:1’s are discontinued items so One SL’s would be a better choice imho. But as @GuitarSuperstar says, consider the Sub first. Your film watching and music listening will appreciate it. 

The neighbours on the other hand might not...

I’d say Sub first, then One SLs.

I got the Sub first and it made my entire experience better. I recently added two Ones and it definitely improved my experience. Without the Sub it wouldn’t “feel” as immersive. So if you can afford the Sub get the Sub first. 

I just recently bought the beam for my small apartment and I’m looking to expand to the 5.1 surround setup. Should I get the Play:1s or Ones for my rears first or the sub first? I want to gradually get to the 5.1 because of the cost.

issue got solved!!