When scaling up a digital marketing agency, should I use in-house retainers or outsourcing?

Hi everyone! I opened a digital marketing agency a year ago in the UK. It has been profitable so far with a good steady turnover. However, it is dependent on ad-hoc projects. I mostly do the work myself when it comes to PPC, social media, content marketing and Facebook ads. Everything else, such as website development and graphic design, I outsource to freelancers. I want to scale up the agency. I was thinking of selling retainers - defined packages paid every month. Maybe come up with one starter retainer for small businesses, one retainer for growing businesses and one bespoke retainer package. I was also looking into the possibility of buying packages from a company which is based in the Philippines. They offer various packages, including SEO, which I can sell and just add my margin on top. My questions is - what do you think - in-house created packages fulfilled by freelancers or re-selling ready-made marketing retainers as bought from a resellers abroad? Does anyone have experience with scaling up a digital agency? Thank you! Slava