You have overhangs in many places.
The x- screw is far too far below the table. This makes the nut bend and chatter. You want the screw as close to the table as possible.
The lateral diagonal supports need to go to the top, not halfway up the sides.
Likewise, a plate along with the diagonal, would greatly improve it.
The y-axis frame member is too small in cross section, in all directions.
Even then, it needs to be solid.
And, despite desires, the round rails will bend unacceptably.
Profiled rails are the correct solution.
For milling, with round rails, you need twice the cross-section.
The y-axis crosswise plate is undesirable. Remove it completely.
-drop the distance to the screw (very good)
-reduce length of vertical supports at corners of table (very good)
Mount the table to the nuts by having a single solid at teach end, below the table, aligned with the x-axis, at the bottom edge of the table. The nuts mount to the solid.
Here, x axis is meant as in the direction of the visible ballscrew.