Can I build my own service in catalog? If so, are there any guides on this?
Configuring the catalog URL(s) in the UI for admins will probably ship with that. (Side note: you can go to the API and change the setting with just a browser, you don’t actually need API keys and curl or similar… User menu -> API & Keys -> click Endpoint link and then navigate to /v1/settings/catalog.url and click the blue Edit button)
Access controls for different catalog items for different people/environments is not in the immediate roadmap. The catalog service runs as a separate API that has no information about what user or environment the request is for.