Is audio quality or video quality more important to you? Connect the Beam to the eARC port if you want the highest quality audio from the PS5 like Dolby Atmos and Linear PCM. Connect the PS5 to the eARC port if you want 1440p @ 120Hz, 4K @ 120Hz, or VRR.

The speakers go on eARC, all other devices go to the other HDMI ports.

ARC and eARC are created in the TV set, not on the source devices. They’re just sending a normal HDMI signal to the TV. 

I’m not aware of any such TV that has that sort of arrangement for HDMI inputs.  They typically only have 1 ARC or eARC port, and the rest have no ARC capabilities.  Did you have a particular TV in mind or is this just a hypothetical?

I’m also not familiar with all the capabilities of the PS4, audio and video, and that would obviously be a factor. I don’t recall what the differences between  2.0 and 2.1 are either.  Beyond that, the answer would depend on other sources for the TV, how much they care about atmos,  loss/lossy, budget and willingness to add additional equipment, etc.

As above, a TV is only going to have a single ARC/eARC port, so you have no choice for the Beam.