Also, NEVER sell your PzIV, it's a great way to build up credits. When you have unlocked everything on it, it becomes Elite and the crew can become real good, real fast, depending on much xp you get in a battle with it. This is done via a tickbox above the crewlist in your garage, says something along of the lines of Accelerated Crew Training.
This option gives the xp you earn in battle(which would normally go into the xp pool for the tank itself for module unlocking) and puts it in the crewmember with the LEAST amount of xp, bolstering it's xp gain. This can get you to 100% decently fast, of course having a premium account helps even more so.
I sadly stopped playing this game, as the RNG mechanics of whether or not i'll penetrate even though i KNOW it's a good shot(i used to have every tank's armor and weapon pen stats memorized) is In my opinion(very important, my opinion, not fact) utterly ridiculous in a tank combat game.
Exactly the reason i'm playing WarThunder these days, because the mechanics are much less RNG reliant, if they're not gone altogether.
But hey, don't let my dislike of a core mechanic of the game give you the idea this game isn't any fun. I had fun while i played, no doubt, but that mechanic kept nagging at me and at some point this summer, it became a detriment to my fun factor.
Also, Pz IC is the best tank in the game, bar none. Not even one of those big fat German Tier X's can give that giant grin on your face that just won't come off no matter how hard you try to suck in it xD
Also, a personal recommendation for tank-line choice would be down the US TD line, via the Hellcat to the T110E4. I stopped when i was ALMOST at the T30, and the T28 Proto was affectionately called the Battle Chariot(it's slow and open topped