If your employer invites you to move to another country then definitely ask for more than what you're currently getting in HK, especially since you've mentioned that you'll be given more responsibilities. And yes, take note of Steve's suggestion.
Main things to consider when moving here: housing and transportation.
Renting a house or an apartment in Hanoi is similar to how it's done in HK. If you want an apartment or house all to yourself, you deal with agents or deal directly with the owner (if you can speak the language or the owner speaks english, which is highly unlikely). Or, as many here usually do, you find yourself some roommates and split the cost. Be prepared to negotiate as the rental market here has gone crazy and prices just keep going up. You usually need to make a deposit in order to "hold" the space. Again, make sure that the terms of the lease is quite clear to you and the landlord. You can also do a search on A.N.H. about previous questions on housing matters that may also be helpful.
Now on to transportation. Like me, I'm sure you have taken for granted HK's efficient transport system. You're going to definitely miss using your octopus card as well as the mtr, buses and ferries once you're here. Your options for transport in Hanoi are as follows: live close to your place of work so you can just walk to work (which is what i do now), take the bus (cheap at a flat rate of 3000VND but crowded), use the reliable taxis (the cost of doing that every day adds up and it becomes an expensive option), rent a "xe om" (motorbike taxis-much cheaper than regular taxis), get a bicycle or rent a motorbike. For the last two options (and even when you go the "xe om" way), be prepared to take on the average Vietnamese motorbike rider and the average Vietnamese driver. The former will come at you from different directions and will signal with a turn of the head to the left or right. The latter still thinks that he's handling a motorbike, will also come at you from different directions and will try to overtake every chance they get. I guess the thing to remember is to be alert. And drive slowly. And get a regulation motorbike helmet before you move to Vietnam.
They have a thriving nightlife here, as I am sure you have read about in this website. Much cheaper than LKF/Soho/Noho/Wanchai too.
Your patience will be tested here many, many times but getting annoyed will get you nowhere (as I have discovered). The Vietnamese are a lovely people. You'll just have to get used to their pace.
It's also a good thing to check this website time and again for other helpful tips from people who have been here longer.
answered about 5 months ago by Ouriel

I would include housing in my contract as mentioned above. If your company agrees, and a serviced apartment is within their budget then I highly recommend this option. I also recommend going the same route with transport. If it is within the company budget, ask for a car with driver to be provided or for taxi allowance to be included in your contract. I'm not sure how big your company is but I'm sure they can swing the above mentioned for your peace of mind and safety if it is within their budget. Wish you everything of the best!