My stand for my sink is 1.5" by 2" lumber. This may be a little on the light side but it was built to go into a tight space. I did drill holes into the bottom of the legs to accept stainless steel nuts and bolts. The hole for the nut is just big enough for it and a smaller hole continues deeper for the bolt. This give me the ability to individually adjust the legs so the sink is stable and drains in the right direction. The bracing is plywood and there are slats at about 30 cm intervals under the sink.
Good luck on yours!