A ruler that controls such vast territories must maintain an exceptionally powerful military force. This is more to deter enemies or internal rebellion than to attack other territories. It is strategically sensible to maintain a strong army as deterrence is more likely to achieve stability and peace. A weak military can result in fragmentation of a country and gives scope for immoral forces to seize power which is detrimental to the society.
Timely sacrifices [ यागः - sacrifice is a poor translation that English has to offer ] to gods ensure timely rains, harvest,etc. These are needed for the well-being of the subjects and hence, the duty of a great king. Also, after the succesfull completion of yajnas like ashwamedha, vishwajit, etc the king used to distribute wealth and grain to his subjects. People from all walks of the society were welcome and were awarded appropriately by the king. These events also helped in socialization and building goodwill.
If the son is unwilling or unfit to take over the reigns of the kingdom, it is the moral obligation of the king to appoint a worthy successor to the throne. Failing in this duty has been the undoing of many empires in the past.