I have no idea you need to ask whoever is building the shower what size and brand they use . I am not sure why the bench away from where the shower heads are makes sense so maybe a bit of info about that and why this particular size Waht type of door how will the floor tiles be layed all factor into this choice . Talk to the person building the shower and the person doing the tile . BTW what are the tiles for the shower floor ? That drawing does not halp to advise on anything .

That’s a lot of bench to squeegee. The shower drain is integral to the waterproofing so the tile professional needs to be consulted. My tiler always uses schluter and therefore a schluter linear drain is used provided by the tiler to my specs.

Forget the brand question for a moment. Are there any best practices for the dimensions of the drain in relation to the shower? For example, you want a drain that is at least 2/3rd the width (making this up) or something like that?

We recently remodeled, our shower is 6’x4’, our linear drain runs almost the complete lengthof the long wall (where you have your bench) We have a bench on one of the short walls. Im no kind of expert, but there was a LOT of work by the tile guy prepping, getting the slope correct, etc

Flo FX or Guru brand linear drains are the sleekest. Schluter is the most expensive, and awkwardest.

I don't get the whole bench-in-a-shower thing. Who sits to shower? Install a toe holder in the corner for leg shaving and call it good.

^^^ 100%. They are always cold and take up floor space.