2nd rule of agile ERP: deploy gradually
How do you eat an elephant? One bite at a time. Swallowing it all at once might be tempting as it has all the potential you need to get into the next edition of Guinness World Records. Likewise, trying it with an ERP implementation has all the potential you need to get into to the next edition of Chaos Report. One way or the other.
ERP software is huge. It contains thousands of features potentially touching every single tiniest aspect of your business. Implementing ERP is about introducing change into your company, and change can be evolutionary, or revolutionary. Your pick.