This should probably go into the documentation at some point but I thought I'd post this on the forum for now.
Hiding /users route from public
In the Settings ACP, select "Make user info private"

Hiding categories from non-registered users
In the Categories ACP, for each category click on "Options" and then "Access Control". For registered-users and administrators, select all boxes like so:

Leave these four options blank for guests.
Redirecting guests to the login page
In the Themes ACP, click on "Widgets" and drag an HTML widget onto the Global Header widget area. In the HTML field, copy and paste the following code and then hit save.
<script>
if (!app.uid && ajaxify.currentPage !== 'login' && ajaxify.currentPage !== 'register') {
ajaxify.go('login');
}
</script>