Where should I put my Era300 as surround speakers

Placing the speakers immediately behind the couch results in the speakers being much closer to a listener. Small listener movements will have a much higher impact on the experience. Temporarily you can try this with extension cords.

There is also a disadvantage to the shown position because the speakers are very close to the wall. You can experiment with rotating the speakers 90 degrees.

Don’t be afraid to experiment.

While trying positions also look at sitting two feet behind the couch.

If that sounds better than closer consider adding a long skinny table (@ 2x6 feet) with the 300s and stands on the rear side of it. The additional distance from the closest 300 may improve balance and imaging over a closer spot

I don’t know how much space is behind the couch.  If the area behind the couch is useable place the stands behind the couch at least 5 feet or more away from your seated position and a couple feet away from the side walls.  Experiment with how much angle toward the seated position sounds best.  TruePlay will take care of any minor asymmetry in the positioning.

would also help to have a couple rugs on the floor to minimize reflections off the hard wood surface.

I do not own Era 300’s but should they be angled towards you? I think they should point towards the TV.

In the position they are in pointing at the TV would mask one of the side drivers on each 300. Maybe rotate 45 degrees and move a bit away from the wall?

I'm not a fan of ceiling  mounting but in that room, and since you are looking at adding a power run anyway that might be a good option. Away from the walls, behind the seating positions, and not right in the ear of anyone sitting on the sides of the couch.

Seems to be crying out for a console table behind the sofa and a couple of floor outlets if they can be installed as the op believes. The speakers can then be placed to the side rear corners of the table.