Setting up Enhanced Packet Cores (EPC) – like the Mosaic5G OpenAirInterface-based EPC – for 4G/5G Testbeds is a complicated and error-prone task. Therefore, we developed the SimulaMet OpenAirInterface VNF, a complex 4-VDU VNF, which upon instantiation builds the components of the EPC from scratch from given source Git repositories. That is, based on the parametrisation, users can easily create tailor-made EPCs for their projects, particularly EPCs based on the Mosaic5G FlexRAN sources. In this presentation, we would like to shortly highlight the solutions chosen to efficiently use OSM for handling the instantiation process, performing telemetry, and debugging issues. That is, we particularly would like to present to the Mosaic5G audience some lessons learned during the ongoing development.