Gutter size matters, but drainage depends on roof area, pitch, outlet locations, downspout capacity, and where water is discharged.
Look for sagging, standing water, leaking seams, loose fasteners, damaged fascia, and erosion near discharge points.
Roof and fascia repairs are easier to coordinate before new gutters are installed.
A useful scope identifies gutter runs, downspouts, color, removal, disposal, and any fascia work.