Maintain parallel lossy and lossless music collections

I have a large music collection. Some of it is lossless files, and some is lossy. I would like to maintain a copy of the collection that consists of the original collection's lossy files, and lossy transcodes of the original collections lossless files. Some assumptions: * I know how to use ffmpeg to convert flac to opus files * I only have flac files that need to be converted, no wav or alac codecs * The lossy files can be opus, vorbis, or mp3 I want to: * Use minimal storage for the the new music collection. I.e. it would link back to the original lossy files where appropriate. * Keep the collection up to date as I add more lossy and lossless files to the original, or update the metadata. * Not have to re-transcode lossless files that have not been modified. I imagine I will need to use some custom scripting to accomplish this, but if anyone has recommendations or tips before I sink lots of time into this, I would be eternally grateful.