Software

I would suggest that you do the add-ins as a seprate deployment as it compartmentalise your work and makes testing a WHOLE lots easier.

So just deploy Office as per normal, heaps of tuts on the interwebs about this kind of stuff, so you should be safe on this front.

As for the plugins you can package them into a MSI, or the latter you could script, but it would be a bit of work.

Anyway, the key part is the links below.

This link will advise you how to enable the addin for ALL users, this is done in the HKLM registry space. I recommened you enable it this way as it much easier to manage/remove later.

http://msdn.microsoft.com/en-us/library/bb386106.aspx

Dont worry about this link too much, but its worth a read and handy to know if you need to fix stuff in the HKCU registry space regarding Office settings.

http://blogs.technet.com/b/deploymentguys/archive/2011/05/31/deploying-custom-registry-settings-for-office-2010.aspx 

http://itninja.us/blog/view/deploying-office-2013-managed-install

Hope you will consider Office 2013 as core application which will be part of base build.. Sould you install these addins in all the machines in your organization?