When to start a new line?



For noob players like me, what advice do you tankers have on when to start a new line?

I ran the American line to tier 5 too quickly in hindsight ending with T1 Heavy, M4 Sherman, M5 Stuart (tier 4) and Chaffee

I then ran USSR line through the T-28 to the KV-1

After that I decided to run the English TD line up to the AT 2 but just got the tier 4 Alecto and will transfer the Valentine crew into once I kick all those 100% crew from "free" tanks that occupy my barracks and then some.

When I get the AT-2 I was thinking about the Japanese line with all the pub recently... but I'm thinking I should just probably learn to play with what I have, right? That prem Chi-Nu Kai loves to kill me...