actually yes.if affects your google ranking so this way you get less visitors and less visitors=less money from adds. just my opinion
it doesn't direcetly but indirectly. you risk your site being banned by google or de-indexed if you have dup content. if your site doesn't show on SERP ranking, your potential visitors can't find your site so your are not making anything or much.
Agree with two above. While using duplicate content will not directly lower your adsense earning (I know from experience), getting traffics to it will be really hard. No traffics means low earning. Unless you buy the traffics from adwords or alike.
Backlinks are king. I have seen several instances of my articles in the serps and my page almost always is the lowest because my new site has much less authority than ezinearticles or goarticles, etc. TomG.