A new hosting company? | Talk Web Hosting

Hi,

We are a software / Internet company and have several clients with WordPress sites that we deal with.
These sites are scattered over several hosting providers.
I've thought … why host them myself, then start to integrate new customers in a controlled manner in search of reliable WordPress hosting.
And so make it a bargain.
I'm pretty sure I'm not the first guy to end up in this position.
Currently, I am thinking and researching the market and the tools available.
I would really appreciate if any of you experienced could give me advice, depending on your experience.
At the moment, I'm talking about less than 10 WordPress sites.
I plan to offer VPS hosting per site.
What are the next pitfalls I should be aware of?
What tools / software would you recommend for a complete solution (including billing)?

Regards,
Michael