I will be installing AGPM in our environment and account to the install guides online you need to install the application under a domain admin account but for the service account you can you a least prividge approach and added the account to the Backup Operators and GP Creator groups..
https://technet.microsoft.com/en-us/itpro/mdop/agpm/step-by-step-guide-for-microsoft-advanced-group-policy-management-40
If I am understand everything correctly one thing about the GP Creator GP is that is does not grant the user full access of already created GP but will on new GP's is this correct. If so with 100 GP's this will be a problem for me