Hi Vern,
You bring up a good point. If you are looking to combine multiple instances but want all the customizations from each of your instances, you will not be able to combine them into one instance. There is some standardization involved when using one instance. For us, because we wanted to get to a point of standardization in our agencies, it made sense for us to go with one instance. Also, we've only ever had one instance so people went from their chaos into Workfront so there was change mgmt and compromise needed anyways. When a new agency wants to join Workfront, we work with them on what they can customize for their office and what they will need to conform to. For the most part, we don't have any issues and the few we have, they are going to be solved soon by Product or aren't that important.
At FCB, we have 13 different agencies in one instance. Now, myself and my partner in crime Kathy are from corporate and our job is being global system admins for the instance. It is part of our job description.
We do have Local Agency Admins who have Plan licenses and an access level that is open to everything except sharing system-wide. This helps with adding/editing users, creating teams and creating/editing Custom Forms for their group. This has helped us out a lot, but there are still things we need to do for them as system admins.
As for the list of things you provided, list of groups and job roles doesn't really matter as they are based on info from our financial system and everyone uses that financial system. For statuses, that is going to be remedied soon when different groups can have different statuses.
Now for the others, everyone has to share the same list. We have a "governance" group I guess you could say that has to approve any changes that are needed. An agency will ask us to change something, we then go to all the SuperUsers from the various offices (normally as a survey). If someone or an office has concerns about a change, we talk to them about it until we can ease their concerns. In the four years we have been on Workfront, so far, there have been no issue.
Sometimes, there are issues with Custom fields. Two offices want a field that is different (i.e. Single Line of Text vs Comment box) but want the same name. So far, they are good about saying "Agency 123's Job Number" and then when building reports changing the display name of the column to just Job Number.
In conclusion, we at FCB found the benefits of cross-agency projects and being able to incorporate Share Services departments more beneficial than having different terminology or lists of items. So we went with the one instance. The company does have to pay for two non-billable system admins, but we have also become SMEs on several different areas of the business and can share past experiences and best practices with the agencies across our global network. We also reduce the admin work that local offices would have to dedicate for their own instances and can help montior agencies for any issues so we can help course correct before it gets too out of hand.
But that has what has worked for us.