Emails - can I send to all or groups?

See Configure private / closed group access, membership and visibility

This sounds a lot like too many messages, but I guess if it works for you then :man_shrugging:

To send group messages read through:

And so, you’d need to adjust the settings for the group to allow messaging:

While to email all users, best bet would be to export your user emails and use a platform like Mailchimp to email them all. Also, messaging TL0 users should also work here, but use group messaging sparingly as you could end up being flagged for spam.

Not sure I understand what you mean here, but Understanding Discourse Trust Levels gives a good read on Trust Levels, and you can also go through the Trust Level section of your admin settings to see the specific details. You’ll find the site settings here /admin/site_settings/category/trust.