I was going to weld the tabs but opted out for a few reasons. I was tired of cutting metal with an angle grinder. The plywood is only 1/2 thick so I was worried about strength. What if someone stands on it and it breaks? And I wanted to make those bolt heads functional. So I cut 5 more pieces of 1/2 plywood, one for the top and one for each side. These are bolted to the inside of the frame and each of the individual panels are attached to that. It's very strong.
As far as weight... I'm not sure. I don't have a way to weigh it at the moment. Need to go buy a bathroom scale or something. If I had to guess I'd say between 50 and 70 pounds. But I'm thinking much closer to 50 pounds than 70.