Second Admin?

How do I add a second full admin account?

Its easy, use Deanos mod, its free

Deanos Tools

My second question: How do I remove / rename the promotion membership level?

You don't. The Promotional membership is one of the 3 built-in membership levels that cannot be removed. But the promotional membership can be disabled so it's not used.

To disable. Go to Admin->Settings->Membership Levels and uncheck the box for Enable promotional membership