If your blog is full of advertising,who will care about this ads?

It will be a pain in my eyes. Do not put too much advertisement at your blogs. Manage your ads.

It's possible with enough traffic you can get private advertisers to place ads on your blog, but most of the time it would depend on your page rank

Yes, if you play your cards right.

I agree with most in here, you need traffic but yes you can earn money from a blog.

Depends on how much traffic your blog got. You can make decent money with any form of ads if you have large traffic.