Administration and easy charging for n customer-->droplet pair.

Dear all: We are new to this VPS world. The thing is: We will have several customers consuming services from 1 to n droplets (SaaS Service). One way to do this (and I’m just brainstormng here so you can help there), is create an interface in our website and to let the user create their droplet with the DO Api and charge for it automatically based on their election. The same with an upgrade they need to do: He/She will choose the “Upgrade” option in our website and the upgrade should be done automatically to a better droplet (or with more cpu, disk etc) and then again we should be able to charge automatically for that change (I mean no manual upgrade and no manual deposit for the droplet should be required because all of that should be already previously configured somewhere else…).

The business diagram is about this: Customer----> 1 to n droplets each of it with a fresh software from us. And there will be 1 to n Customers doing upgrade anytime they requires it.

Hopefully it does exist a better solution to implement it…

What is the best way to manage this universe of customers-droplets to ease the pain from the administration point of view based on your experience? It does already exist one software that can do this easily and that can be embedded in our website (appart from the DO API) that can in charge of all of this administrative tasks?

Thanks in Advance!, Roberto