Twitch may seem like a strange choice, but it's possible to stream Twitch from VLC, and chat via IRC, with no proprietary software, not even proprietary Javascript
Youtube Live is widely used, but can't interact with Free tools AFAIK.
Zoom is widely used and understood, but is 100% proprietary, other than people using the phone dial-in.
Other options? BBB is interesting, but I can't find any low cost option for hosting one off events.
So please vote, or provide alternatives!