A complete site redesign is a huge opportunity. I would start by IGNORING what you have going on your current site. Spend 20 minutes staring into a mirror in an attempt to hypnotize yourself into forgetting that you know anything about it. Start by defining the flows and messages for each key audience.
Audiences Put together a list of key constituencies. Customer groups, audiences, markets and partners. This usually includes: Existing Customers, New Customers, Stale customers, one-off Product Buyers, Media, Talent/popential Hires, Partners, Investors, etc.
Vision Interview the people who represent the vision of the company. This includes all the senior management. Here is a checklist of Q's You can ask the same questions different ways.
a. What is the company valued for?
b. what are our sustainable points of differentiation?
c. What do we do? (seriously - ask this)
d. Why do we do that? (Apple makes computers, they make them in order to make things incredibly great to use) - you need to find the WHY Specifically,for each product type.
e. How do we deliver ?
f. Establish points of credibility for the value proposition (features etc.)
Content Now, you need to work out how to get the informaton from a-f into a context that connects with the problem you solve for each constituency. I would also look to defining the selling sequence, in general prioritizing the information for your information architecture.
Seriously, this is a great opportunity to make a valuable contribution to your company- and it could afford you access to the top people in the organization. That access is needed to really do this well. You might find it interesting to record the interviews.
Now, you can revisit the existing content to see what components solve the communications challenges you have uncovered in a way that is still relevant.
Purge and Simplify I would encourage you to put the greatest emphasis on simplicity. Almost NOBODY is going to drag their tired eyes across much drivel about YOUR products Let them get the top level and cut anything repetitive or non-essential. Keep it real. Remove the jargon and corporate speak if you can.
The best way to unravel this is with a story told in pictures and/or video.
Specifically, to answer your question - Almost everyone could be involved to some degree. I do hope this is helpful, and not overly simplistic.