What is way too much? I take around 4000IU per day. Which just about brings my blood levels into the “green” area in blood testing.
Your 4000IU isn't too much. Lots of the brands you see in stores are 5k for daily supplementation.
By what metric? Jeez. People, you need to get your blood checked. There is no one-fits-all dosage. In winter, 4000 IU/d was enough to raise my blood levels well into the excessive range.
I fully agree that supplementation should always be combined with both blood testing and also a general medical evaluation.