first time autoblog question

i found something with low competition and 6600 monthly searches on google.

i know 6600 searches isnt a ton but the product itself has alot of underage & stupid users that will likely click on adsense.

i think i can get on the first page of google easy and maybe even the first slot.

the real question is what formula do people use to estimate what they might earn with adsense?

i am hoping to make $30 a month minimum with each autoblog but i dont even know how to begin to estimate my earnings.

a 2nd question that kind of relates to the first.

can i use a generic domain like SleepieGirl.com for example which has many varied topics and still expect adsense earnings.

does each domain need to focus on 1 main topic or can i have 50 categories and a shit ton of posts in each?