Hanoi to HCMC over xmas and New Years for 20 days

hi guys,

I would really welcome your feedback on this schedule I have created for my trip to Vietnam.
Me and my boyfriend are flying to Hanoi and leaving from HCMC, we have to skip Sapa because i had a surgery on my foot, so no point going into the mountains for bushwalking. My boyfriend wants to get a bit of rest on the sun as well and we like adventure, good cousine and just discovering new things.

24.12 Hanoi 10pm arrival to the airport
25.12 Hanoi water show, around the town, the usual
26.12 Tam Coc 1 day trip, evening back to hanoi
27.12 Hanoi - Halong Bay
28.12 Halong Bay - Hanoi - overnight train to Hue
we wanted to see the cave in Phon nha ke, but not sure if it is worth it considering the time and different reviews
29.12 Hue and around
30.12 Hue - transport to Hoi An in the evening
31.12 Hoi An (it seems nice idea to spend New Years there ??)
1.1. Hoi An
2.1 My Son and back to Hoi An - overnight transport to Nha Trang
3.1 Nha Trang
4.1 Easy Riders for 3 days to Da Lat
5.1 Easy Riders
6.1 Easy Riders - Da Lat - overnight bus to HCMC
7.1 HCMC morning flight to Phu Quoc
8.1 Phu Quoc
9.1 Phu Quoc
10.1 Phu Quoc - Mid Day flight to HCMC
11.1 HCMC - afternoon flight to Sydney

I could earn day somewhere to spend more time on PQ or could fly within the country to save some time, please give me your opinion.
Also, I checked the accomodation on PQ and it seems that everything nice has been booked out. I could imagine to not go there and stay on a nice beach somewhere on the mainland - any suggestions?

Cheers,
Veronika.