Steel tubing for a workbench questions

I’m planning a build for a workbench that can accommodate a rolling mobile workbench underneath. The design will probably be just a simple square table frame.

My questions are the following:

  1. It seems like square tubing would be the easiest for a beginner like myself because of large welding surfaces. What size and gage tubing should I use (I won’t be doing anything crazy on the table like working on engine blocks or anything, but still want it to be sturdy).
  2. What type of bracing would be beneficial? Corner bracing with tubing/sheet metal? Horizontal bracing on the back/lengths?

I would use 1.5" square pipe with a wall thickness of 14 ga