To arrange the sentences meaningfully, let's analyze the given sentences for each question.

### For Question 1:
The correct arrangement is:
**C - D - B - A - F - E - G - H**

The coherent paragraph would be:
1. "Dear Sam, I trust this letter finds you in good spirits."
2. "In essence, this journey has been a profound one, broadening my horizons and instilling in me the importance of flexibility."
3. "Yet, the rapid rhythm of city life can sometimes be quite daunting."
4. "To begin with, the cultural richness is remarkable; every day brings a new interaction with individuals from diverse backgrounds."
5. "Moreover, the potential for personal and professional development seems boundless."
6. "The urban lifestyle is truly a vibrant one."
7. "Eagerly awaiting our next meeting! Best wishes."

### For Question 2:
The correct arrangement is:
**D - B - G - F - A - E - C - H**

The coherent paragraph would be:
1. "Urbanization in Vietnam has brought numerous benefits to the country's socio-economic development."
2. "In addition, urbanization has spurred improvements in infrastructure, such as better roads and public transportation, which enhance the quality of life for city dwellers."
3. "Last but not least, the growth of cities has fostered cultural exchange and innovation, contributing to a more dynamic and diverse society."
4. "In conclusion, while urbanization presents challenges, its advantages are pivotal in propelling Vietnam towards a more prosperous future."
5. "To begin with, the concentration of services and industries in urban areas has created more job opportunities, leading to a reduction in poverty."

These arrangements create a logical flow of ideas in both cases.