Chartjs-ChartJS custom doughnut chart not showing in version 2.6.0

For question #1 the issue is with the this.getDataset().metaData inside the draw function. It is returning undefined and so the function under Chart.helpers.each doesn’t execute

Try this.getMeta().data instead.

EDIT:
For question #2, you can refer to this other Stack Overflow question:
Charts.js: thin donut chart background