OP: If you are going for the cleanest-looking front end (fewer cables/wires), get a Di2-compatible handlebar and use the bar-end junction box instead of the box that fits under the stem.
PoorInRichfield notes, the BT dongle is pretty useful, and not very expensive. It's also tiny, and can be integrated into your system almost invisibly.
Regarding Sram: yeah, wireless is awesome. Those huge derailleurs are not so awesome.