Simple rule of thumb is 1-1.5x the loader lift capacity as ballast. Split between the tire fill, wheel weights and 3pt. About 1/2 of the ballast on the 3pt. That will at least get you close.
As others have said, the task impacts the ballast amount and location. A full loader will lighten the rear tires, where a bottom plow or big disc will lighten the front. Fer example... My TLB has a 5000 pound loader lift to full height. Filled tires add about 600# (partial filled), wheel weights add 1200# and the hoe is over 3000 pounds. That's essentially the same as the lift capacity, and it's still light in the rear with a full bucket due to geometry. This shows up when filling a front bucket and having to back up a hill. Flat out, it don't! Why? The front weight is farther out front than the rear weight is out back, so it teeter-totter's around the front axle. But after dumping the bucket, backing down a hill is scary as the front gets light! Just can't be perfect for all things all the time!