Will redirect redirect e-mail too?

I've just registered 4 domains, one of which is fully hosted, the other three redirect to the primary. The primary is set up to use Google Apps for e-mail, etc. If someone sends an e-mail to user@mydomain.com, will it forward on to user@mydomain.org (which is what I'm hoping will happen).

No, redirecting a domain only affects web hosting. Email hosting is separate, so you'll still have to set up forwarding addresses behind the forwarded domains.