nextcloud tries to do everything so it settles for good enough instead of doing some things really well. the text part of chat works well, its webrtc struggled for me even with the high performance backend. i set up a jitsi server with only jwt auth going through the nextcloud integration on mine to get around that limitation.

there is a guest join by link feature in talk. though nextcloud can also be set up to use outside oidc. so you could allow people to log in with their existing accounts. making it easier for people who would struggle registering.

nextcloud will lower the barrier for entry on your users with the ‘single interface’ feel. its just gonna shift that effort onto you to scale past like 10 users.

All in one solution, your describing nextcloud. Though if you started in signal maybe its not the right solution for what you’re doing? if the group is official enough for there to be donation and tax records maybe go nextcloud.

https://github.com/stoatchat/ is an option, its made good progress since discords first try at age restrictions.

setting up a few matrix servers is probably the more secure way to go. and either mumble for voice or jitsi if you want voice and video chat capabilities. decentralize and avoid a situation where one self hoster leaving or one domain seizure shuts everything down.