I hear you can buy galvanizing spray after you've welded you apply it.
You can also grind down the weld edges to remove the Zinc so you can weld, but that's a bit more risky.

I'd be looking at building a spinner since I see it as being the most simple design for me that contains moving weaponry, I'd have it designed so it would have front interchangeable weaponry so I could still go to contest which bar the use of spinners.

I was thinking of 3mm - 4mm Checkered mild steel plates, I always liked the look of footplates on a robot.