Advice on setting up an online division

We are looking at starting an in-house client side online department, except rather than set it up like an online marketing dept, we would prefer to set it up more like an agency as we already have a strong marketing team. We manage a multitude of subsidiary businesses.

Does anyone have some good advice on what type of specialists are required at the start of a project like this, and how many?

Initially this would be a small team that will grow over time. It would be involved with web development and design, non-transactional, transactional, as well as e-commerce websites within retail and leisure.

My initial thoughts are:

A/c managers/directors
SEO/Usability specialists
PPC specialist
Affiliate mkting specialist
Email/Analytics software specialists
Web dev team
Interactive designers

This is really the beginning, so I just wanted some feedback before I started to scope it out!