MicroUSB is acctually recommended to be placed on the underside.
You will notice that when interfaced with USB chips as D- and D+ lines up.
Pinout names is for topview on toplayer, but moved to bottom layer it will be flipped around for correct pin out too.
The USB connector is this one:http://www.mouser.com/ProductDetail/FCI ... 2fag%3d%3d
Recommend to use Littlefuse SP0503BAHTG (a SOT143) for Vbus, D- and D+ connected to shield.
It's shown in picture and try to use the same layout as D+ and D- should keep same lenghts.
Use max 10uF cap on Vbus to stay within usb2.0 specs.