More details are needed...
Are we talking thumblogger crap-a-rama blogs or domain based blogs?
You are asking a lot. Expect to pay for it...Unless you are talking about pumping out whatever and hoping for the best...It takes more than a day to make a good blog and get it started....
What are niches?
Who are your sponsors?
So far you are talking building a blog design, graphics, writing, seo...
And, How much ya got? $$$-wise....
