ETL Platform for Ad Data Integration

I'm building a config-driven, source-agnostic ETL platform that extracts advertising data from multiple ad platforms (starting with Meta Ads, then Google Ads) for multiple marketing agencies, where each agency manages multiple ad accounts. I'm looking for an experienced consultant who has implemented Meta Ads API and Google Ads API integrations at scale and can help define the correct architecture and onboarding process. Note: I've used the Meta and Google APIs before. This new project involves design decisions, permissions, and so on, since I need to access data from accounts that aren't managed by me, but by other marketing agencies that will be contracting this service.