One “buyer” can realistically handle all things platform related for 10 clients, especially at that spend level. Your bottleneck will be relation and strategy (account management, business, creative, etc. ) in order to have a chance of growing and keeping these clients. A. A super lean team with just a buyer and a designer could work. Ideally to maximize efficiency you add someone that handles all communication with clients. B. You add either another “buyer” or designer with someone that communicates with clients. I think the designer and media buyer role is relatively interchangeable depending on the needs of your clients, but at 5k a month it should be pretty light weight. Ideally, I think the optional strategy is to have one person lead the team that has all skills including FB ads, creatives, and client management, and have them manage a team of lower tiered employees. In theory it sounds good but that position is extremely difficult to hire for.