You've got to care and feed this system, because the technical and functional issues never go away. Make sure you understand your infrastructure requirements and have properly sized the infrastructure before starting. After you finish, do a post-mortem. Write up lessons learned and things you could have done better. Don't lose the quality of the experience in both positive and negative terms.
Project management is crucial.
We had managers and then teams for each component of the software modules. In addition, we had a manager for the technical side of the project. ERP's complexity isn't so much of an issue, rather it's the change brought on by the system. Maintain and control project scope and be ruthless about it. Keep critical project dates in mind.