I drink around 7 to 12 cups of coffee per day and I cannot function properly without my coffee everyday especially when I'm working.
I would say anymore than 13 to 15 cups of coffee per day would be too much but some people including my Grandma used to drink 20 cups of coffee per day and she lived a very good long life of 110 years old before she died.
She drank lots of coffee up until she died at 110 years old so you're not gonna be harmed by drinking a lot of coffee but some people might experience different results.
Coffee is supposed to be good for your health and heart health as well as preventing heart disease, heart attacks, strokes etc.
So by drinking lots of coffee you can be improving your health.
But I would stop drinking coffee at least 1 to 2 hours before bed because coffee especially if it has caffeine will keep you awake and prevent you from sleeping.