Dormer window seat/storage bench question

[Preena]

Hello all! As the thread title says, I’m planning on building a window seat in the dormer area of my daughters room. She wants me to build out the entire area and have storage underneath. The dimensions of the space are 5’ 2.5” X 4’ 4.75”. I am planning on making it freestanding rather than bracing it to the wall. In fact, due to the size, I’m actually planning on making essentially 2 separate benches and screwing them together to create the continuous platform for the bench cushion. My question is about support. I’m planning on using 2x4’s for the frame and 3/4” plywood for the top and exterior. I’m assuming with these dimensions that one horizontal top center and bottom center support in each bench, with 3 vertical supports in the front and the back, and one additional vertical support at each end would be sufficient. Is that correct? Also, when making the benches, does it matter support wise if I make the frames with the edges of the 2x4’s facing up and down or is it better to have the face side up? I’ll be using pocket hole joinery if that makes a difference.

Thanks! ~ Preena