There is no such a thing like a linear dependency on provided space or bandwidth and actual usage (or as you call it “Ratio Demand”).
The Community has an average statistics though, thus you can use this Community Earnings estimator to get an idea:
But in general the renting a VPS is not a wise idea. As you already know, the space and bandwidth are used by real people, thus no predictable income or usage. But you should pay for the server every month.
In the first 9 months your node will receive not a big amount of money for the service.
If your datacenter have other nodes in the same /24 subnet of public IPs, they will be treated as a one node, so profitability will be very questionable.