I think you can set a wide range of targets:
-average aero coefficient on your windtunnel aero maps
-aero balance setup window
-total ballast available
-cg height, inertial properties of tha car
-stiffeness of the tub (even if we are now out of the stiffer, the better)
are just the first, most general that come to mind.
These key chararcteristics may flow down to "local" targets like: "reduce paintwork weight by 50% compared to last year", that would impact on cg and ballast.
I think paint is 3-5 kg on a complete f1 car, why not shed a couple of them?