Main site with path

I have a szenario I don’t know how to solve. I have installed a MU WordPress site.

First problem – site path

I have two sites “www.powerdoo.com” (site1) and “www.powerdoo.com/de-de” (site2). But I want that my main site also has default path, so the result should be “www.powerdoo.com/en-us” (site1). Inside the network “sites” settings it is not possible to change the path for the main site. How can i solve this?

Second problem – web.config redirect

It my first problem is solved I now want the URLs Redirect like this:

http://www.powerdoo.com -> http://www.powerdoo.com/en-us
http://www.powerdoo.de -> http://www.powerdoo.com/de-de

Can anybody help me how I have to write a rule for this?

Thanks Steffen