using google keyword tool you can find keywords with low competition and as for how many you should choose i would choose about 5 keywords.
In My opinion you choose maximum 10- keywords for Home Page because Your home Page is the main part of website
I suggest you go to ezine articles and search for your related keyword. find the top articles and you can use that keyword for you article marketing. ezine articles is by far the best way to bring up your stats
Not more than 6 to 8 keywords. Diving them up in secondary and primary. Also use no more than 2 keywords per page.