I recently spent 3 nights in beautiful Nong Khiaw (March 2017). I know from experience that it is tough finding up-to-date info on NK so I thought I'd share a few tips here.
*How to get to NK from LP - We opted to take the 9:30 am public minivan from the south bus station (includes pick-up from your guesthouse). You will see signs posted at every travel agent for public minivans with prices ranging from 70K kip to 85K kip - you should be able to negotiate down to 65K like we did. The minivan is air-conditioned, left right on time, and surprisingly only took the advertised 3 hours even with a toilet stop (ask your driver to stop halfway and he will).
*Where to stay in NK - There are tons of guesthouses here, most pretty basic and cheap. If you're not fussed to stay at one of the few fancier options, you can just book a place when you get there. You will see that most of the backpackers coming off the public buses and minivans do this. You'll pay less than you will if you book ahead. I like booking ahead so had a reservation with Meexai Guesthouse (US$15/night) - it was basic but good.
*Where to eat in NK - There are several good food options in town. We found the food was really good quality and surprisingly much better than what we found in Luang Prabang. The wait times can be quite long at some of the places because everything is cooked-to-order and it's usually just a one-woman show so don't wait till your starving to show up! We really liked Alex restaurant (go early for dinner b/c the wait will be very long when the place gets jam packed). Noymany is also a good option for breakfast (banana crepes and french toast done right!) and lunch - plus it has a river view. Deen restaurant for Indian makes a nice change for dinner (the set menu is really good value).
*Things to do in NK - 1) The viewpoint hike is amazing, don't skip it. It's a pretty tough, steep climb up (with ropes to help in some parts) but the views are incredible. It'll take roughly one hour to hike up and 50 minutes to come down. 2) The Patok caves are okay, we didn't find them that impressive but others we spoke to did. We enjoyed the walk there and back though. 3) Rent kayaks at NK Adventures. They only advertise their pricey kayak excursions but you can get them to rent you a kayak - they'll give you a discount if you only take it out for 1-2 hours. Great way to see the river. 4) If you're hot and want to swim, there is a restaurant/camping site just outside of town towards Patok caves that has a nice, large swimming pool you can use for 30K kip. 5) You can watch movies at Delilah's Place each night so long as you buy something. 6) There are many daily excursions you can book with the travel agents in town for hiking/kayaking, etc, but we found them really pricey. If you're on a budget, you can rent bikes, scooters, or kayaks and explore alone.
*How to rent a scooter - There is only one place in town (surprising I know) that rents scooters. It is just over the bridge on the east side. They seem to only have a few automatic scooters (the rest were manual) that they rented for 100K kip/day (or 70K kip for a few hours). If you want an automatic scooter, you need to go early in the morning to ensure you get one.
*How to get back to LP from NK - If you're not into taking the public bus (takes 4-4.5 hours), the public minivan only departs NK at 1:30 pm. If you need to get back to town earlier than that (like we did), you can book spots on a 9:30 am shared minivan with NK Adventures. They weren't willing to budge on price so we had to pay 80K kip per person. Still, a much better option than paying for a private minivan (~500K). The van was pretty comfortable, air-conditioned, and the driver stops half-way for a toilet break. It took just over 3 hours.
Hope you find this helpful. Enjoy your trip to Nong Khiaw, it's an incredible place!