I even have the E75 for 3.480.000 Credits, fully upgraded and can you believe, I still play the Loltracktor!
Enjoy the game and find your playstile
Something just for fun and how not to play:
http://www.youtube.com/watch?v=_-5vpAE3iMc
http://www.youtube.com/watch?v=H5oREL_wMuw
I have spend 20€ to get some Gold, why, simple: I need some Garage slots. They cost normaly 300 Gold each, but if you wait, they have it for 150 Gold per slot. It happens sometimes.
And as Gepard said, you will need the credits later, but, if you get into a nice Tier 5 Tank like the KV1, M4, or the StugIII or Tier 4 Matilda, you will earn some Credits. I still play without premium and enjoying it most of the time. You will get later with alot of damage dealing some 40.000Credits per game, but each shot will cost you some 1000. Even the Tier 6 KV1S cost 1000 per shot, but deals some 400 Damage. If I need some fun, I have succesfull games, but alot of Credits are lost for AP Rounds. The Last battle I have left, the ammo cost me over 35.000credits but dealt alot of damage. So I recieved a + of 1100 Credits ... yes and that in a Tier 8 Ferdinand.