Dave and Vikki, How do your teams work today and what things are being reported now vs what you want to do? Workfront can absolutely scale to large orgs and can handle incredible workloads BUT what you do with the data once it is in Workfront is something different. Here are a couple scenarios to keep in mind while scaling up:
Project Templates can be great, but who applies them and keeps them up to date?
One thing I've learned about marketing departments is that they usually don't have their own Project Managers. Therefore, while creating great project templates can reinforce process be sure to balance that with the overhead increase on resources who aren't project managers. This is especially true if you have a high velocity (which most marketing groups do).
Custom Forms can accommodate all kinds of data, but how do you want to report on it and who enforces that it will be filled out?
This is similar to what Vic was posting about regarding making sure you know what data you want to report on. Whether its a form on a request, issue, task, or project - make sure you're once again balancing data vs. overhead vs. velocity. Also, try not to overload your forms with data points because your organizations need will morph pretty quickly once they start seeing it. I'd start very light.
Request Queues are for Requestors, not those that manage the Queue.
This is a tricky one because Workfront CAN automate many things related to queues, however - make sure it is a good experience for those you're looking to get the requests from. It may be really neat that you can create all of those topic groups and routing rules but if the requestor doesn't know how to ask for what they need then adoption will not go anywhere.
Workfront doesn't take the place of actual conversation.
I know, I know - it's the shiny new toy but in all reality one of the biggest mistakes I've seen with deployments is to substitute Updates for good, old-fashioned conversations. Yes, the decisions made in those conversations should be included in Updates, and Yes, Proof is Awesome but many rollout's experience "speed bumps" a month or so into them because folks thought the no longer needed to talk to each other. This is will happen on a large-scale rollout - just be warned.

Overall, large-scale rollouts are really fun and you can see improvements pretty quickly if you have a solid training program. Just make sure your org is anticipating and staffing for the increased overhead with actually managing projects. Organizations don't realize they have this gaping hole until they start seeing (or missing) the data once it's captured in one spot (ie Workfront). Workfront doesn't create the need, it exposes it. If you have any questions, feel free to reach out. John Albaugh