Using a fan isn't necessary, but it is well advised. The initial slight wiff of air from even a 500 rpm fan makes a big difference. And you won't ever hear it unless you live in an anechoic chamber... and maybe not even then.
The case you have selected has almost no ventilation. That coupled with no fans is just asking for trouble. If you want no fans, this is a much better case:http://www.techpowerup.com/reviews/LianLi/PC-T1R/
Slipstream makes some nice 500rpm fans. Why not go with more conventional cooling, but use those 500rpm fans. You won't hear a thing... and they use almost no electricity. They are nothing.
There is something to be said for the Seasonic PSUs with a fan. The fan doesn't kick in unless you hit a 20% load. The only time that fan will move, is if you need it, and then you will want it moving.