Based on the provided text, here are the answers to the questions:

1. **How many ethnic groups are there in Vietnam?**
- There are 54 ethnic groups in Vietnam.

2. **Where do the Kinh people mostly live?**
- The Kinh people mostly live in the central coastal delta, the Mekong delta, and major cities.

3. **What is the population of the Tay?**
- The population of the Tay is around 1 million.

4. **Which ethnic groups have the smallest population?**
- The ethnic groups with the smallest population are Brau, Roman, and Odu, each having several hundred people.

5. **What do most ethnic peoples mainly live on?**
- Most ethnic peoples mainly live on wet rice cultivation and farming techniques.

6. **Do the ethnic minority groups have the same culture, religion, and belief?**
- No, each ethnic group has its own culture that is diverse and special.

7. **How is the culture of each ethnic group?**
- The culture of each ethnic group is distinct, diverse, and special, reflecting their unique beliefs and practices.