Thailand forum

Dear SE Asia travellers,

My girlfriend and I are planning a trip to Vietnam and Thailand, arriving in HCMC on the evening of 8 July and returning home from Bangkok on 8 August. I've put together an itinerary and would be very grateful if some experienced travellers could cast their eye over it. Recommendations, suggestions, changes would be greatly appreciated. We've included a few internal flights to save time. Here we go...

Day 1 - HCMC
Day 2 - HCMC
Day 3 - HCMC (day trip to tunnels)
Day 4 - Mekong Delta (over night stay)
Day 5 - HCMC
Day 6 - Nha Trang (fly from HCMC)
Day 7 - Nha Trang
Day 8 - Nha Trang (Sleeper train to Hoi An via Danang)
Day 9 - Hoi An
Day 10 - Hoi An
Day 11 - Hoi An
Day 12 - Hue (easyrider from Hoi An???)
Day 13 - Hanoi (fly from Hue)
Day 14 - Hanoi
Day 15 - Halong Bay
Day 16 - Halong Bay
Day 17 - Hanoi
Day 18 - Hanoi
Day 19 - Bangkok (fly from Hanoi)
Day 20 - Bangkok
Day 21 - Bangkok
Day 22 - Bangkok (sleeper train to Chiang Mai
Day 23 - Chiang Mai
Day 24 - Chiang Mai (over night trek)
Day 25 - Chiang Mai
Day 26 - Ko Sumui (fly from Chiang Mai)
Day 27 - Island (Ko Pha Ngan/Ko Sumui/Ko Tao
Day 28 - as above
Day 29 - as above
Day 30 - as above
Day 31 - as above
Day 32 - Fly Surat to Bangkok to home

Specific questions:
1. Is it too long in HCMC given our time frame. Would it be better to take a day off and put it somewhere else?
2. Is an overnight stay on Mekong highly recommended?
3. Should I take a day off somewhere to add on to our stop in Hue?
4. Given our timeframe is a two night Halong Bay package appropriate or would one night suffice?
5. Should I take a day off Bangkok and add it on to Chiang Mai?
6. Is it worth doing to Pai to do the trekking or will Chiang Mai suffice given our timeframe?
7. Is there much added benefit from island hoping or should we maximise our time on one island and explore it as much as we can. If so, which island out of the three?

Thanks in advance.
pm