Very interesting to see this idea built and ready to go.

I went the same route you did with the table (the tape on MDF approach doesn't hold small parts well...), excepted for the Y-Axis, which was doubled up to avoid deflexion when machining far from the centerline.
I see the linear rail on the left of your picture. Any plans to upgrade de C-Beams or just some stuff lying around?

 

I like the idea of building the table out of extruded aluminum as opposed to MDF or even a solid aluminum plate because the weight savings for one is huge plus as you mention you now have a different surface to hold your parts plus ways to attach various types of workholding such as vises or clamping. I hadn't noticed other builds filling in the slots of all of the beans like your photo shows. That's a smart thing to do too.