Fake and gay.

Why did he need to invade poland, if things were going so well?

He invaded to retake the German property that was lost in WW1. Do not forget, Hitler was a soldier of distinction in that war, and he wanted to reverse the outcome.

He probably also wanted the coming war with the Bolsheviks to NOT be on German soil. He was well aware the Bolsheviks were arming for a military push across Europe, and Poland would be their first target. He wanted his military on that front.

When he had retaken the land lost in WW1, you'll notice he stopped. The USSR, on the other hand, invaded Poland with no claim at all to the property they stole, and yet the (((allies))) never suggested war with Russia.

Germany, once at war, pushed into Russia in a lightning-strike to try and cripple them on that front & destroy their military. It almost worked, but they took too long, and winter foiled them. To do this, they necessarily had to cross the Russian occupied regions of Poland.

Remember, Bolsheviks = Jews, and the governments of the west were controlled by Jewish financiers…and then it all starts to make sense.  

Is it better to invade when things are going bad?

The Allied forces (ie Jewish Allys)

Were looking for any excuse to go to war with Germany to please their Jewish masters.