+21 days itinerary in Vietnam advice?

Hi all, my partner and I will travel for Vietnam from the 17th of June until the 117th of July, entering through Hanoi and exiting through Ho Chi Minh. We're into hiking and also beach, but want to also experience the local culture and life in Hanoi and Hoi An. Wanted to share the itinerary we made with you in case you had any recommendations to add or places to swap. We were also wondering if we should visit Cambodia or not, but we're a bit afraid of the weather during the weeks we're visiting. Thanks!

Day 1|Hanoi|

|Day 2|Hanoi|

|Day 3|Hanoi|

|Day 4|Sappa|

|Day 5|Sappa|

|Day 6|Sappa/Bac Ha|

|Day 7|Ha Giang|

|Day 8|Ha Giang|

|Day 9|Ha Giang|

|Day 10|Cao Bang|

|Day 11|Cat Ba|

|Day 12|Cat Ba|

|Day 13|Cat Ba|

|Day 14|Ninh Binh| - tam coc

|Day 15|Ninh Binh|

|Day 16|Hoi An/Da Nang|

|Day 17|Hoi An/Da Nang|

|Day 18|Hoi An/Da Nang|

|Day 19|Hoi An/Da Nang|

|Day 20|Nha Trang|

|Day 21|Nha Trang|

|Day 22|Da Lat|

|Day 23|Ho Chi Minh|

|Day 24|Ho Chi Minh|