Because the X-Carve isn’t a 10 ton behemoth, the general guidance we users have come up with is to keep the cut depth half of the bit diameter or lower. Even when stiffened, the machine generally won’t support much more than that because of spindle power, belt drive, and lack of stiffness.
As for Y axis bracing, I made 3 braces for each side and integrated a mirrored acrylic belt dust shield in the design. It’s nice and stiff and works well for me. Y Axis Braces and Belt Dust Shield