Rather than write about the whole process of building the visualization, which Microsoft has already a good job of on Github pages and in their video, I wanted to just highlight a couple of items that I had trouble finding information for.
1. Getting to the DevTools interface for deploying : This was quite frustrating because I didn't see any documented ways of getting to a 'dev enabled' powerBI UI. Finally I had to glean this from the demo video. Look at the URL around the 8 minute mark. It includes a query parameter called DevToolsEnabled=True. This is the magic setting to turn on dev tools so you can compile your viz online and try it with datasets.
2. SelectionManager : This is the entity dealing with selections on any of the visualizations and communicates the same to the rest. While the sample code in AsterPlot referred to a utility.SelectionManager, this code wouldn't compile. I eventually came upon this discussion that made it clear that the public service and github projects were not in sync.
Other than this, my challenges were around not knowing TypeScript at all. That took some getting used to but was not too painful. I quite enjoyed the typed use of scripting.