If you haven't already bought that PSU, then don't. Yes 400W would be enough, but get a better made PSU. I just looked at the reviews for a 400W Hipro on newegg, most are saying the PSU died on them. If you want my pick of a good PSU that is very well priced for what it is, I suggest this one http://www.newegg.com/Product/Product.aspx?Item=N82E16817438012
If you haven't already bought that PSU, then don't. Yes 400W would be enough, but get a better made PSU. I just looked at the reviews for a 400W Hipro on newegg, most are saying the PSU died on them. If you want my pick of a good PSU that is very well priced for what it is, I suggest this one http://www.newegg.com/Product/Product.aspx?Item=N82E16817438012