Minumun number of hubs to start earning with adsense?

I think that Misha has just over twenty, but he's one of the highest earners here. You should search and read Misha for an understanding of how.

It is not the amount of Hubs, it is your good and unique content, that is searched for, and read on the world-wide web. In order to have any earnings, Google, must find your platform feasible enough to place ads. When ads are placed by AdSense, the readers of your Hubs, must be interested enough in the ads, to go and read them, that is where AdSense earnings come from.

It depends on how popular your hubs, and back linking too.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.