I think this will need to be split. First implementing all the chat features, then maybe conversation settings and other smaller things and then the calling. Otherwise it's way too much work to implement and review.

https://github.com/nextcloud/spreed/issues?q=label%3Aoverview+label%3Aenhancement should be a pretty complete list of (new) features that get added each release.
IMO it makes sense to try to implement new features and existing/old features at the same time. If we'd only implement old features then the client isn't a good alternative to the existing clients and if we only implement new features then the basic stuff everyone expects isn't present which also doesn't make it a good alternative.