Hey Shin,
If you plan to get more cultural shots, please make sure you spend more time in SaPa. its a great place to explore. go for trekking to Lau Chai, Tavan, and other villages. there are few tribes living in different villages, if you interested, you can do homestay in village, they have the accomodation for tourist in Tavan. make sure you ask their permission before you taking their pics, at least smile to them (not available for candid =P) Some of them still believe that pictures can take away their soul. Silver waterfall in SaPa will be good for scenic, and a long the way to the villages, you'll see great view. If you plan to do tough trip, you can go to Fansipan. For hotel, i highly recomended Boutique SaPa Hotel, its good value hotel with excelent service. Bring some school stationeries with you because: 1. they need it either for themself or their kids 2. it will save you from the ladies/cluster that following you along the way to sell their souvenir.
Ha Long Bay is beautiful, specially if you good in taking landscape pics. you might consider to stay in 1 of the island. kayaking there is one of the recomended activity.
Hanoi and HCM are interesting, i spent only few hours there, cant give any recomendations. For staying, you might want to check out Rising Dragon II in Hanoi. perfect services.
Have Fun!!!
