Block Registration, and Automatic Email Notifications

Great forum - experimenting with it now...

(1) We have a finite number of people that we want as members. How do I block all future members from registering? I'd like only those invited to join.

(2) Is there a way to automatically send emails to all members when a new post is made, AND every time a reply is made to a post?

Thanks for your help!

1) Users & groups>Users options
Allow new members:
choose whatever you like admin or none.

2) For that they should watch a topic. The link is at the bottom of every thread. They can access it in profile>preferences
Topic(s) being watched tab