Wow, that is quick progress. That's a very attractive frame. Nice build quality. What is your plan is to mount the stepper motor?
It seems like building welded steel bases is the latest trend. One thing that people doing this should keep in mind is that while the gantry itself is very rigid, the overall machine rigidity does depend on the strength of the base as well. Even though the wood base in the plans is just built from plywood, it is incredibly strong. After I first built the wood base, I turned it on its side, with the electronics door area against the ground. I then climbed on top of it, standing at the extreme unsupported cantilevered part. And jumped up and down. It felt like jumping on a solid block of wood. It is very, very stiff.
Not that I'm implying that your base doesn't look strong enough. I'm just saying that anyone building a steel base should make sure there is no perceptible flexing between the side uprights.
Keep up the good work, its looking very nice. And keep posting pics, please!