Sure, Vietnam is a wonderful country to explore with its rich cultural history, picturesque landscapes, and flavorful cuisine. Here's some travel advice to help you:

Best Time to Visit:
For Hanoi and Hoa Binh, the best time to visit is during spring (February to April) and autumn (October - November). Da Nang and Ho Chi Minh City have a tropical climate, so November to April are good times to visit to avoid extreme heat and heavy rainfall.

Route and Accessibility:
You can start your journey at Hanoi, then head to Hoa Binh province, which is about 2-3 hours by road. Afterwards, you can fly from Hanoi to Da Nang (1 hour 30 min flight) and finally reach Ho Chi Minh City via a short domestic flight (1 hour 10 min).

Altitude and Acclimatization:
These cities are not located at high altitudes, hence acclimatization won't be an issue. But the hot weather between June and July requires you to stay hydrated and wear sunscreen.

Accommodation and Booking:
Book accommodations in advance. Vietnam offers a vast range of accommodations from luxury hotels to guest houses.

Clothing and Essentials:
Light cotton clothing is recommended due to the humid tropical climate. Don't forget your hat, sunglasses, sunscreen, and a good pair of walking shoes for touristic exploration.

Health and Safety:
Ensure you're up-to-date on routine vaccines. Be cautious about street food, and remember to carry any personally prescribed medication. Avoid discussing sensitive political topics.

Local Etiquette and Respect:
Vietnamese people are very polite and kind, and they appreciate the same behavior from tourists. There are no strict requirements about clothing (except in temples where you need to cover knees and shoulder), but decent dressing is appreciated. Respect local traditions and customs, avoid loud conversations and maintain cleanliness.
Remember to lower your voice and avoid public displays of affection.