I recommend you to book a hotel for just one night as your arrival, then you can take a change the next day. Through photos on internet, you cannot know which hotel is really good, better come, check and decide (to stay or not ) Many nice hotels with reasonable prices are available, from North to South of Vietnam.
Re currency, if you have a Visa/Master card, it will be no problem, there are many ATMs, you can withdraw Vietnam dong. If not, you can change money directly at the airport.
Btw, puma_1977's info is quite beautiful, just follow his tips and hope you have a wonderful trip in Vietnam.