Posters are automatically logged in - can't be

[dismas]

I'm not sure I understand your entire post but to answer the first couple points...

Check vBulletin Options > User Registration Options > Moderate New Members > Yes
and
vBulletin Options > User Registration Options > Verify Email address in Registration > Yes

As for being able to log in when registration is turned off... That's not what turning registration off does. It means that current members can still log in but that new members may not join your site. There's a difference between logging in and joining.