Seven needs one dominant piece
With seven frames the eye needs somewhere to start. Make one piece clearly larger than the rest, at least 16 x 20 against a set of 8 x 10 and 11 x 14 frames, and place it off the exact centre so the composition has direction. Seven similar-sized pieces read as wallpaper rather than a gallery.
Stagger the rows, not the boundary
A 4 + 3 arrangement puts a gap in the lower row under every frame in the upper row, which is what makes it feel composed rather than stacked. The outer boundary should still be a clean rectangle; only the internal joints stagger.
Plan the whole block before the first nail
Seven positions means seven chances to accumulate error. Work out every left edge and floor height first, mark them all from a single datum, then hang. The planner exports exactly that: a coordinate table with each frame's left edge and bottom edge measured from the wall's bottom-left corner.