On a VPS or Dedicated server you just select remote email server when setting up an account. For WP hosting you may need to contact support, but it all depends on where you set your nameservers. You could manage these settings from your domain registrar, but if you'd prefer you can just set your nameservers to point to your KH server and KH support can easily handle that request.
Yes, WP updates can easily be disabled in WP Admin by adding a disable updates plugin or add a line of code to wp-config.
http://www.wpbeginner.com/wp-tutorials/how-to-disable-automatic-updates-in-wordpress/