Best Practices that streamline an Agency Running Facebook Ad campaigns for 50+ clients?

Hi Everyone! This is long, but I wanted to lay it all out - as I’ve been struggling determining the best path to use for scaling and can find no clear examples.

Details:
Assuming all clients are in the same niche, and running similar lead generation campaigns, how do other high volume Agency’s run a clean, organized, repeatable structure in Facebook BM?

Different options I’ve reviewed when trying to build a clean scalable operation within Facebook BM:

OPTION 1: Manage Using Client Ad Account/Page - client onboarding/ both are account and FB page admin permissions needed.

OPTION 2: Manage Using Agency Ad Account / Client FB Page - only client Facebook page admin needed

OPTION 3: Manage Using Agency Ad Account / Generic FB Pages - no client onboarding or permissions needed.

There are MANY pro and con considerations for each option, but I didn’t want this post to be a book :)

Really, I’d love to find those that have mastered a clean process for not only what is above, but also SOPs for a scalable service model for a high volume of Facebook clients.

Thank you!
Roger