Your config is a little confusing given you've got multiple webmin-created sites however given that sites-enabled/000-default is empty we'll concentrate on the only other enabled site - sites-enabled/webmin.1211729846.conf:
Code:
<VirtualHost *>
DocumentRoot /var/www/apache2-default
<Directory "/var/www/apache2-default">
allow from all
Options +Indexes
</Directory>
UserDir "public_html"
</VirtualHost>
Change DocumentRoot to the directory in the home directory you want to serve, and edit the <Directory> directive to suit. Then make this web directory, and all parent directories, have read/execute permissions for Apache (user 'www-data') and see how you go...
Mathew
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