Optimum weight vs optimum body shape are different things - kinda like in people. 6 ft tall and 200 lbs can be very different depending on body composition. A healthy ball python shows symmetry from its slimmer neck to its heavier body. They should appear "plump" and feel appropriately heavy, but not obese. Shoot for a good body shape.

I'd say a good feeding schedule would be a small rat once/week with the occasional skipped meal being fine.