Open Access has matured for journals, but its uptake in the book market is still delayed, despite the fact that books continue to be the leading publishing format for social sciences and humanities. The 30-months EU-funded project HIRMEOS (High Integration of Research Monographs in the European Open Science infrastructure) tackles the main obstacles of the full integration of five important digital platforms supporting open access monographs. The content of participating platforms will be enriched with tools that enable identification, authentication and interoperability (via DOI, ORCID, Fundref), and tools that enrich information and entity extraction (INRIA (N)ERD), the ability to annotate monographs (Hypothes.is), and gather usage and alternative metric data. This paper focuses on the development and implementation of Open Source Metrics Services that enable the collection of OA Metrics and Altmetrics from third-party platforms, and how the architecture of these tools will allow implementation in any external platform, particularly in start-up Open Access publishers.