There are English courses?
There are, in Spanish, Portuguese and Italian.
At the moment Duolingo only has courses in Spanish, Portuguese(beta), French and German. So no, not right now.
Yes, there are. You can find them at your settings page.
Well, the reason they have English courses is because you may think that only Americans use Duolingo, but people all over the WORLD are using Duolingo (does this explain?)