Panzer III/IV won't see Tier VIII. Tier VII is the maximum it will see, though that will still be tough.
I'm not too familiar with the Panzer III/IV, and to be honest looking at the stats it doesn't look that stellar. One thing that does appear nice about it is its speed though. You can try to get into aggressive positions with that speed, but considering your current experience with the game I feel like this might be a bad call as you won't be able to work those positions good enough.
I'd try to play it as a mobile support. With that speed, hopefully you can get to positions where you can exploit flank shots. Don't be too aggressive until around the mid game. At that point (when some tanks have died) you can look for potential openings to exploit with the speed of the tank. Get around behind tanks and hit their rear. Don't stay engaged with big heavies if they are going to turn around and deal with you. Don't be afraid to do drive bys, popping off a few shots and then zooming away.
Your gun depression isn't super (6 degrees). You can work the ridgelines a little bit with it but not as well as many of the other mediums.
Your camo rating isn't bad (as long as you don't fire your gun), but your view range is atrocious. If you are wanting to play a scouting role, you'd need binos equipped. Note that when spotting, if you spot a tank and then that tank gets damaged by a friendly, you get XP for "spotting damage."