The lighting was a fun exercise as well.
When I had the bike over at the bike shop I pulled a wire through the frame all the way to the dropouts.
From there it took some soldering, looking up several techniques to connect wires on Youtube, and lots of heatshrink.
It works well and is hardly visible:
Not much left now.
I have a few things I still want to change but I'm taking the bike on vacation next week and the budget is gone for now.
Time to put it to the test in the Alps!