With Agile becoming more and more popular, many customers have adopted it as it allows you to react quickly to changing business needs. In my experience, I have seen Agile ERP projects being more successful than the waterfall method. Every customer has his/her own version of Agile though. Understand the customer's current process, and tweak it to the version that would work for the ERP project. For example, if they are creating all the tasks on the board and physically writing them down, you may want to switch to the electronic format for better collaboration with remote teams.
Plan the tasks 4-6 weeks ahead, and build a backlog of things to be done after the requirements or Gap/Fit sign off.
It is very important to have unified tools and processes across the board.
Generally, there is misconception about Agile; Agile does not mean no documentation. You need to enforce using standard templates for all the deliverables (for example, functional design, technical design, and so on), and do not take any shortcuts using the Agile methodology as an excuse.
Schedule frequent reviews (demos) with the business owners for each sprint cycle.
Break the implementation team into smaller scrum teams by relevant areas. You would have cross-functional dependencies across the teams.