A quick note...
Taking the rep++ option when accepting mission rewards also increases your rank by a magnitude with the corresponding super power (federation/empire/alliance). So long as the mission giver is actually aligned with a super power...
So if you're looking to rank up to get a Clipper or Corvette you should pay attention to the reputation options when handing in missions.
On one hand, you could accept 1,000,000 credits and rep++ for easy money and moderate reputation.
Or....
You could settle for just 150,000 credits and rep+++++ which would put you much closer to that dream ship.
It pays to plan ahead.