My own welded steel router is built from 50x50 and 100x50 steel box, all 3mm wall thickness (search for "AVOR" on this forum for a bit more detail). Overall size roughly 1800x1000 with a cutting area of about 1500x750. I'm happy with the overall strength of the machine but if I were doing it again, I would use at least 4mm, maybe 5mm, wall thickness steel. Not for strength but mainly to control vibration and resonance in the tubes. It also makes it easier to bolt on the rails, etc, as 3mm is a bit too thin for a decent tapped M5 hole. 10mm wall thickness seems way too much for the uses you suggest - that's heavy stuff!