Now it depends how you want to do it.... you can have lots of sites with little traffic from search engines (you can check product from my sig if you want to know how to do that). or you can have one site with lots of traffic (this is harder, in my opinion).
I see this is already too difficult to build a site which brings good amount of money. I'm now building 2 sites and it is enough. I don't have time for content when I build more sites. Two is a good one.
I'd just concentrate on one site. Getting new contents and maintaining many sites would require very hard work.
it depends on your hard work frd.... if less sites then less hard work .... and if many sites then more hard work needed to be look after. i too have few many sites which i take proper care when needed to be updated and advertised.
Start small and then once you get the hang of i you can go big.. I started with one site myself and have expanded my site portfolio as I learnt more.. Starting with too many to begin with can take a toll
You have two answers that seem to be the most prominent. Start out with one site, get it rolling and then move forward. Or if you have the time, then open 3-5 sites and run with it. It is going to be more about you and if you are willing to put in the time to keep all the sites up and running with fresh and unique content.
bro, it's simple...don't bother to create just one blog and blogging till death..thats's sucks for adsense..even with high paying create lots of free blogs, set and forget and do simple tag n ping, get links using comment kahuna and don't forget, only select easy niche first...it will motivate u coz u will be earning fast with that, even with low earning at first hehe...i know people do black hat using blogspot creating 1000 blogs and producing up to $100 -200 per day...
i've got 12 websites right now.. and i'm earning like 6-7$ in adsense daily i'm planning to take each one to earn 1$ and then i'll take them to 2$ each and so on...
I have already create more than 10 blogs on blogspot and two websites for adsense. I am planning to create more sites. I enjoy to create new sites. It's true that doing SEO for multiple sites is tougher. But advertising on free classifieds with multiple sites is easier. Free classifieds are major source of my traffic. I don't depend on SE.
Just do one site. It will make it easier to optimize and it will have better quality than making several sites.