Feedback needed for one month (about) in Thailand and Vietnam!

Hey! I'm leaving for Thailand next week and would love if someone could give me feedback for my route so far! I feel pretty confident on the first half in Thailand but I feel like things start to look questionable once I get to Vietnam. I am booking a one way ticket so I have flexibility. I am trying to aim for 42 days max.

• After 50 hours of travel (yes, I have 2 long layovers) I will arrive in Thailand.
• Bangkok (3 days) and then an overnight bus to Chang Mai
• Chang Mai (4 days) and then flight to Krabi
• Krabi (3 days) and then train/bus/taxi (2-4 hours) to Khao Sok National Park
• Khao Sok National Park (2 days) and then bus/van (2-4 hours) to Phuket
• Phuket (3 days) and then flight to Ho Chi Min City
• Ho Chi Min City (3 days) and then sleeper bus (18 hours) to Hoi An
• Hoi An (maybe 3 days) and Da Nang (maybe 2 days?) and bus (12 hours) to Nihn Bihn
• Nihn Binh (2 days) and then bus (2 hours) to Hanoi
• Hanoi (3 days) and the Ha Giang Loop (4 days)
• Fly back home from Hanoi

I feel like I should cut a city from Vietnam because it looks busy (except Hanoi and Ha Giang Loop those are non-negotiable). What do you think? Any feedback would be appreciated! Thanks!