FWIW, this is how I changed login redirect and tabs on a K2 hack site. I will have several authors and public commenters will be required to register as subscribers. The login redirect now goes to the main blog page and the admin tab reads “My Profile” and goes to the profile page instead. Novice type users never have to deal with the dashboard, though I can get there if I need to.
((I changed /wp=admin/ to /wp-admin/profile.php/ and Site Admin to My Profile.))
This was the simplest approach and worked great for us. The commenters and the other people who write posts at our org can click on “my profile” and go to something familiar that makes sense, without being thrown by landing at the dashboard. I just let people sign up on their own and change the roles of internal people who want to post.