वैदिक काल में राजा को प्रशासनिक कार्यों में सहायता प्रदान करने वाला सबसे प्रमुख अधिकारी कौन होता था?

In Ancient Indian Statecraft, Kautilya's 'Rajamandala' theory primarily deals with:

The First Buddhist Council was held at ______.

Which ancient Indian text contains references indicating that population counts or census-like records were maintained in ancient India?