if you're immediately redirecting, there's no point having the sitemap on the root, unless you're only redirecting specific pages/visitors. and you want a 301 for real seo benefit. 302 tells the SE's hey go to this other site for the time being. 301 says "i've moved so take all the good things I have going for me (including sites linking to me) and point all that goodness at this new location."
use 301 permenant redirect, don't even think about using 302, it is a like a way to tell google " punish me plz"