Flying into Hanoi, looking to spend time there and to go about as far South as Hue/Hoi An. Just my girlfriend and myself, and we are looking at a solid 9 days of travel/vacation when you take out travel time. We saved extensively for this trip, so we are both ready to put forth $700-$1000 US for budget, but looking at other threads, it doesn't seem we'll need nearly that much! Here are my questions/concerns/wants:

Travel

In general, we are most interested in memorable sights and experiences. We tend to try to stray away from extremely touristy areas whenever possible, but I realize some things are must see and are still always crowded. We are not interested in where the good shopping is, or where to find the best night clubs.

Hanoi - We may look into the student/youth tours as they serve a good cause and have great reviews on Tripadvisor. The girlfriend wants to see Perfume Pagoda, and I think the mausoleum would be cool. Beyond that, we are up for suggestions!

Sa Pa - Would love to get out here for a day. I'm concerned about the weather though. Some sites say November is a perfect time of year for it, other accounts say all they were able to see was fog, and the roads were extremely muddy.

Ha Long Bay - This is a major want for the girlfriend, and I'm pretty excited too. I know to avoid the "too good to be true" deals, but I've read that there are the two day trips that take you out to the more remote/scenic areas. Is there a way to find the better guides or trips? Is Cat Ba worth seeing or spending time at?

Hoi An/Hue - I want Hue for the history, the ruins, temples, etc. Girlfriend wants Hoi An for the beaches, and I wouldn't mind it for the fresh seafood. There seems to be differing opinions on these, too. I've seen some accounts that Hoi An is just far too touristy, or that some say they were underwhelmed by Hue. (I still think Hue will be cool)

Also important is what are the best methods from getting to these areas? I've seen suggestions for overnight bus or train, or even taking a short flight for pretty cheap.

If there's anything else on the way or in between these areas we didn't mention, let us know! I've seen that newer, less touristy areas are being discovered as hidden jewels that we may have missed.

Lodging

We are not looking to stay anywhere super fancy. We've heavily considered some of the hostels, even. The one in particular started by Australian back packers that offers guided excursions sounded really fun. We may want a little more privacy to be uh, romantic, so to speak, though. I realize we can get great hotels for ~$20 US, but I also don't want to be whisked away from the authenticity of the trip.

Food

Most important! We want as much authentic Vietnamese/SE Asian food as possible. Lots of pho, fresh seafood, etc. We're going to try lots of street food. Am I crazy to be intrigued by the "eating a beating heart of a cobra" thing? I'm very adventurous and sort of want it just to tell the story when I get back. Let me know what else is must-try or what to avoid.

General

I am going to try to haggle when I can, and know about the certain taxi companies to avoid when leaving the air port. I heard from a Vietnamese-American friend that $2 bills are like gold over there, often times worth more than face value. Is this true? If it is, I could go to a bank to get a bunch of new, crisp $2 bills for special tipping or haggling.