Chris,
Contact ESRI or your ESRI sales rep to discuss this.
The way you have outline the process you would likely be in violation of your ESRI AGOL general terms and conditions - Except as expressly permitted by ESRI, you cannot "sell, rent, lease, sublicense, distribute, lend, time-share, or assign Services or Esri Offerings".
However, each client can purchases their own AGOL accounts and needed licenses. You as consultant would be allowed access, with clients permission, to manage these accounts but independent of each other. AGOL is a great platform for what you are looking to do, you just need to deal with the legalities.