प्रसिद्ध इतिहासकार गौरी शंकर ओझा के अनुसार, गुप्त शासक किस वर्ण से संबंधित थे?

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?