Not for me. I average between .50 cents a month on adbrite and about $2 bucks a month with adsense. Thats on single sites. But I am not an SEO expert and I read that if you setup a site and put your adsense on it within minutes of it being built you only get penny's per click. You have to wait a few months with good content and then drop in your adsense pub id after a few months and then boom, your clicks are worth a buck or two. But still it amounts to traffic and my clicks are due to people doing it on purpose so you have to cross your fingers that your content is good. Only cause the truth is they click on them cause they like your site. People aren't stupid like we want them to be, and just click on our adsense cuz they are stupid and we are somehow smarter than them cuz we know how to make a website. Reality bites but it's true. Sorry if I burnt out a light bulb or two but hey...it's the truth. Life is not that simple.
You wont make much...its too much work, too much bandwidth and space on your host and does not make enough money unless you get millions of impressions per month.
Just do a listing site but not too general, something niche In my country a simple site like http://mudah.com.my will boom in no time.
It depends, are people generally more interested in using your service or clicking on ads ? With image hosting, usually none of your adverts would be associated with the places where the images are shown so you pay for the traffic and not get any returns. For file hosting, you will usually spend a great deal of money on bandwidth as files may be huge and the percentage of people clicking on ads are low. You will also have to constantly battle cease and decease request to take down illegal contents. All in all, none of the above would give you good income unless you charge for your services.