I did this exact flight last Christmas and had no issues with TPR access and F Lounge access in T2 before our flight to HAN.
We couldn't get a room in any of the transit hotels so we ended up sleeping in the TPR and J Lounge - staff were very accommodating with blankets and pillows. If you don't end up at a transit hotel then I'd recommend getting over the back left corner of the J Lounge early enough to get yourself a good spot on the couches. Take some ear plugs with you if you're a light sleeper as the lounge can be noisy right up til 1am - we had screaming kids running around the lounge at 2.
In Hanoi, there was a massive line for Visas on arrival and we ended up waiting over an hour to get our Visas. We did the Visa on arrival, but there are other options too - you can either send your passport to the consulate or arrange a 'VIP' transfer on arrival. I used Vietnam Visa Pro who were very prompt with my Visa letter.
My TR on my Hanoi travels ->
http://www.australianfrequentflyer....-photos/hanoi-hua-hin-bangkok-some-80350.html