All of my work benches are 2x6 and plywood.
I don't know what all tools you have, but you can do alot with just a circular saw, speed square, and a couple of clamps.
Height really just depends on what it's being used for. Assembling a 3d printer, yeah, I'd want to sit.
I'd make a top sized for the printer footprint plus a margin, with a beefy 2x6 frame, then throw a braced 4x4 post under each corner. Later, pull the posts and turn it into a chest of drawers for parts, accessories, filament, etc