I am looking for some benchmark on the Total People Cost (In-house + Outsourced) of Customer Service Department as a percentage of Annual Revenue.
The answer to your question is going to vary greatly depending on the product or service that is being offered, at what level, to what audience, in which industry, and with what degree of support the company intends to offer. Each business model and industry is going to have a different set of standard figures. And then the quality of the product will also govern how much support demand should be expected.
Can the pharmaceutical business suit you? All you need is in it.