Few question regarding Nextcloud

I wanted to start it for a large community but there are some issue and i am very new to it so here are my few question

how to set a default limit on Storage for new user ?
Using Wasabi where i can find option regarding that?
Talk I loved it but it suggest all registered user to everyone is there any way only know user can talk to each other means you have to give them your username instead of it suggesting all user name to everyone.
using different storage for Live video calls and voip calls as i am thinking to use digialocean space for it so video call could be better?