I'd go with at least a #6, #4 recommended. If you're welding you'll be running 20-30 A continuous. Then you could have an air compressor or heat pump turn on at the same time, drawing another 50-60A or so. And this doesn't include the peak motor start-up currents which are higher yet. You want to size the wire so you don't get a significant voltage drop to the panel, and on out to the tool or equipment. Use this
wire size calculator to help you size it out., based on distance and expected max. peak amps.