Thanks for the suggestion! I've made it!
Basically, for the 2nd UHV,
1. Wideness. India needs to be wide enough (12+ cities), since Buddhism cannot be spread to certain cities (I tried like three times or so and failed). So plan ahead for all these settlers.
2. Dual religions. Only focus on Hinduism and Buddhism. Do not build temple for minor religions. They may leave your cities at some time!
3. Khajuraho! This is really helpful to build a temple of your state religion. My path is firstly Hinduism, then convert to Buddhism.
4. Whip and whip. Since India has low production, you may need to live with Slavery for a long time until you get 2nd UHV.
5. Islam. Founding Islam may help you to build one or two extra temples on time. If there happens to be a GP, Islam Shrine would help it spread to some of cities for free!