Ravenshaw, I've created a TW Chat group on Discord, set it private (invite only) and basic member levels (Admin, Moderator and Member with permissions to text chat / voice chat etc.)
Private means I have to generate an invite link - I'll post the link for you and other moderators later, then for members (and seekers) later if it all works.
It looks as if you can connect to discord by web browser or by Discord client, the latter offers some extra features - allegedly!
Discord requires you to register an account using your email and you set a display name for your account - I'd suggest people use the email they registered here and use their displayname her as discord username to helpp us identify legitimate joiners and assign them to the appropriate user group.
I'll post more in private areas here once I'm ready to test it out. So far it's been pain free to setup and may be the best option.
The Blab chat option will take longer as it needs the TW database to be changed, then the Blab software added and integrated with our database - it then uses userrgroup permissions here to allow members to use it - no registering elsewhere, but possible slow down of server etc.