Workbench height, depth and the one feature I would not skip

Height: knuckle height standing straight for general work (about 34 to 36" for most people), 2 to 4" lower for hand planing, bar height for electronics and detail. Depth: 24" for a wall bench, you cannot reach further anyway. Length: as much as the wall allows.

The feature: a solid overhang of at least 3" on the front and ends so you can clamp anything anywhere. Most store-bought benches have an apron that kills clamping. A doubled 3/4" MDF top with a replaceable hardboard skin on a 2x4 or 4x4 base is cheap, flat and dead.

Power strip screwed along the back edge, a light directly overhead, and a pegboard or cleat strip above it.