What is "a lot" of traffic and what kind of server load are you expecting? Will your customer need a dedicated server? Will a basic VPS be enough? Right now I don't think that you have enough information about what your customers will need and you don't seem to know enough about web hosting in general?
In your situation, for the time being, I think that I would pawn the customer off to a hosting company and take a referral fee. As you grow and learn more about hosting, you might be in a position to offer hosting packages yourself.
Not trying to sound harsh, I simply believe that we should focus on what we know and gradually learn so we can expand into other areas.