Just found an excellent set of articles on German tank markings and colours:
This first link has the tank colours for the different years of the war, so it looks like I can initially get away with grey tanks from the start of my campaign, until the start of 1943. It will let me play a lot of games before I really need to worry about tank upgrades and cammo schemes.
So my tanks will be numbered 221, 222, 223, 224 and 225, designating them from the 2nd company, second platoon, 1st to 5th tank respectively, from the 1st Battalion, of the Panzer Regiment they are from.
Now, I won’t be painting numbers on the turrets of my tanks, so I will have to come up with a way to tell them all apart… maybe a small base with numbering on the top? I don’t want too large a base, so will need to think about this.