I am an advertising agency - which VideoHive licenses do I need?

I own an advertising agency. I make videos for social media for multiple Clients of mine. I wanted to buy elements from on video hive this will be an extension in after effects. Which license do I buy? And do I need to buy multiple licenses since I will be using the extension for multiple social media posts for multiple clients? I am very confused on this.

You definitely need at least one license per client. As for multiple licenses per social media post… you need one license per end product (per post), but if all of the posts are part of a series, then you can use one license up to 52 times over the course of a year.