Facebook Ads - Experienced in Agency Environment

I have many clients wanting to start Facebook Ads with my business managing their Facebook accounts. Whilst I can setup Facebook Ads using business manager, power editor etc, I am not sure how to set this up properly in an agency environment.

Some clients have Facebook, some dont, some have Business Manager some dont, some dont mind pressing a few buttons some do, its such a complex situation, for me!

If you have worked in an agency environment before, managing clients Facebook accounts using business manager etc, I would love to hear from you.

I would want two things; first you explain to me the correct process, second, build the end solution together with my Facebook and my clients Facebook. This could take a few days to a few weeks.