Do not leave reporting and data migration until towards the end of the project.
Two activities that it pays to start early on any ERP implementation project are:
Data migration scoping
Report scoping means defining the 'inventory' of reports that you expect to need for your solution. This includes defining KPIs and the mocking up the graphical dashboards that management will need. It's easy to underestimate how much work this will entail. So start early.
Reporting is a solution domain that crosses other functional domains and requires its own 'lead' to manage the workstream.
Data migration scoping means defining the range of data migration 'entities' that will be needed from the as-is to the to-be solution. This is mainly a scoping excercise as most data can only be migrated towards the end of the project to ensure it is current, but some data must be migrated into the TEST envirment early to faciliate any development and testing of CR deliverables.
Data migration is also a solution domain that crosses other functional domains and requires its own 'lead' to manage the workstream.