What is the best way to use it as an reseller hosting?

I don't work for them, with that being said: You "own" the host, you can have as many applications (as it can hold) - keep in mind it is not unlimited and you might have to increase server size in order to accomodate more and more customers. Each customer of your would be an application. and you can even create a project for each customer and have their application inside. There is no automatic way to create new accounts and link it to billing so you have to do that manually (as far as I know). It is still a very good hosting provider and worth the while.