What are the consequences of having multiple wives as a Hindu in India?
The consequences may include a criminal conviction as Christian and Hindu polygamy is unlawful (except for Goan Hindus) - only Muslims may have multiple wives:
Section 494 and 495 of the Indian Penal Code of 1860, prohibited polygamy for the Christians. In 1955, the Hindu Marriage Act was drafted, which prohibited marriage of a Hindu whose spouse was still living. Thus polygamy became illegal in India in 1956, uniformly for all of its citizens except for Muslims, who are permitted to have four wives and for Hindus in Goa and along the western coast where bigamy is legal.
A polygamous Hindu marriage is null and void. While the punishment specified in Sections 494 and 495 is applicable, it is rare if the first spouse does not have an objection.
Suppose I am Christian / Hindu and I decide to use law-2.
In India, a Christian or Hindu cannot rely on Muslim legislation to lawfully dissolve a marriage.
Christians use, as applicable, sections 10 or 10A of the Divorce Act 1869.
Hindus use, as applicable, sections 11 to 14 of the Hindu Marriage Act 1955.
One consequence of not "entering into any legal process" is that the spouse could petition for a lawful divorce by claiming, for example, "spousal desertion" - sections 10(2)(ix) and 13(1)(ib) for Christians and Hindus respectively.