Alone through Vietnam

In my opinion if you travel alone, it is better to book private rooms and airport transfer then join group tours. It will save much cost for your trip, also you can DIY but you should have plan detail, you can take bus to other destination but local bus is crowed and not stop right place you want to visit. We use Indochina Best Travel for past trip, you may contact them if you need to arrange some tours.

With 2 weeks, and assuming that you also want to spend some time in Hanoi and Saigon, its going to be very difficult to fit in all the places you are looking at (and no chance at all to include more).

Day 1, arrive in Hanoi
Days 2- 3 Halong Bay cruise
Days 4 - 5 Sapa
Days 6 - 7 Hanoi
Day 8 fly to Danang, travel on to Hoi An
Days 9 - 10 Hoi An (maybe include My Son for half a day)
Day 11 fly to Saigon, or travel overland
Days 12 - 13 Mekong Delta
Day 14 Saigon
Day 15 fly out of Saigon

You can see by this possible itinerary how rushed it will be. I would probably drop either Sapa or the Mekong Delta to allow a bit more time in other places.

In Sapa, you can homestay at H'mong people but you should check out homestay before booking because a lot of homestay in there do not local people. Halong Bay sounds good, you should book cruise tour from Hanoi which will get more promotion than Halong, you can check out Halong-Bay-Tours to know more price and services as well

Myson: by all means do it on your own or you might regret it.

Hire a motorbike and leave before dawn. The site and the museum open at 6 AM, so try to be there 5.45. After 8.30 at the latest mayhem breaks out. Just imagine tour buses after tour buses with people crawling all over the place.

Better light in the morning anyhow and it will be much cooler.

For the haggling with the driver: Point out that he will be back in Hoi An by 11 am or 12 noon. So he had almost the entire day for doing his usual business. This helped me to get a good rate. The roads are good, just one short strip along the major national highway over the big bridge was not so pleasant. There is a second museum along the way and it is free. Visit that on the way back. Some nice pieces. Worthwhile.

I m not too impressed by Sapa. But that's just me. You might consider another location with less people visiting. Sapa is pretty much tourist central.

I managed to get an early morning minibus tour to My son that avoided the crowds, and was back in Hoi an by 11 am. Sapa was my first stop in Vietnam, and I found it a bit odd. Why is there a Scooby Doo statue in the gardens above the town? It has to be said, this was the quietest place I found in Sapa. I much preferred Ninh Binh, where it is easy to avoid the crowds.

Mp63, that's good info. Do you have more details on the minibus? I had no idea about it and opted for the bike which I definitely not my preferred mode of transport. Any add-ons greatly appreciated!
THANKS!

I got picked up by a minibus at Danang railway station, that was heading for Hoi an. The driver was a Mr Dong, who had a brochure of tours. He took me to Hong Cong homestay, where he was known. I asked the mama at my homestay to book me the early start My son tour with Mr Dong. I never saw him again, but after climbing the wall to get out at 5.30 am, I was picked up by a Moto, and ferried to a minibus up the road, and on to My son. We arrived soon after the sunrise, the place was empty, and totally quiet. I didn't wait for the guide, and headed off to take photo's before the Koreans on our tour climbed all over the monuments taking selfies. It was beautiful in the early morning, and avoided the heat of the day. There was an option of doing part of the return journey by boat, but I was dropped off near my homestay in Hoi an by about 11.30, so plenty of opportunity for afternoon activities, or in my case beach.
We picked people up from various hotels in town, so if your guesthouse or hotel can't arrange it, try a travel agent. I can't remember what I paid, but unlikely to be more than 10 dollars.