Primary DNS for the host 1
Secondary DNS for the host 2
And I can add another 3 and 4 different DNS hosts that to make sure that my website will never stop.
That will not work as expected, given that DNS info is often cached. Some of your visitors will still experience downtime if one of your servers is down.
As for email, you can add a second MX record that points to your second server. Yes, you should setup an email account on that server as well. http://en.wikipedia.org/wiki/MX_record