I'm about to do my first Di2 build and everything looks unfamiliar. All of the stuff online seems to be from the first generation of Di2, so aren't that helpful anymore.

Goal
I want the cleanest Di2 install and don't care about the cost.

The Plan
Run Ultegra Di2 with no visible battery or junction boxes. I think that means I will have a bar end junction A box that is connected to the STI levers via a Y Connector(?). A wire from the bar end junction box goes down the downtube, around the bottom bracket, into the chainstay and connects to the junction b box. Wires from the junction b box connect to the rear derailleur, front derailleur, and seat tube battery.

Questions
Is the Di2 Battery Charger something that goes on/in the bike, or is it just something that allows me to charge the battery with an outlet?

How does the Wireless Module fit in the diagram? I know it goes in the handlebar, but what part of the Y Connector does it attach to?

How do you attach the battery to the seat tube? I see that there are some specific adapters, but they only seem to be for a small number of manufactures. If I buy a "Di2 ready frame" that includes a seat tube, should I assume that the seat tube can accept the battery?