What is the preferred translation of A leader serves into Latin?

My suggestion is dux servit ductis, "leader serves those (s)he leads".

1. What is the Latin word for leadership?
2. What does Memento componere Aequus mean?

What is the Latin word for leadership?

There is the noun ducatus, which can mean leadership.

What does Memento componere Aequus mean?

From Odes 3.29. Memento componere aequus. As with most Latin, it can be hard to put into English succinctly. Roughly it means: Remember to settle things calmly.