I feel it should have, if not the full business plan, a subset of it to convey your vision to everyone. Company policies and procedures. An explanation of web technologies, perhaps how your products work. This may allow someone hired to answer the phones to learn enough to be promoted to other positions - that is if the person takes the initiative.
I think a handbook is very vital, it shows your employees that you are serious and organized, I don't think it would be good to just throw them out there without anything to go off. I think the most important things to include are your policies and how you expect your employees to present theirself and how you want them to represent your company.
My preliminary handbook includes work hours of all employees, our server specs, various software we will use on a day to day basis(live chat, whmautopilot, etc), specific duties of each employee, our goal as a company, and a few other things.