Bit of an update.. went to the 'secret spot' up north yesterday, and it was awesome. Proper surf up to about 4ft, clean cross-on wind, and only 2 other kites on the whole beach. Had a couple of great sessions there, well worth the $10 cab ride each way. I had been trying to get there on a scooter but fitting kite, bar, pump, harness, board & wife was a bit too challenging for me. Spent the day there and had some great fun in the surf. Finding a syringe with needle still attached in the beach rubbish was a slight downer though.

Hired a bike today and found a place on that beach for 300,000 Dong which is about $28 per night, including breakfast delivered to the room.
Also be aware that a lot of prices are quoted in US dollars, and you can't get US dollars, you you have to pay in Dong. They convert it at the US->Dong rate so it ends up costing more than US->AU->Dong would (which is how we tend to work it out in our heads).
Tan you can't get a visa on arrival - you can for Laos/Cambodia/Thailand but not Vietnam or China due to being Communist I think.
Taxi, Feb probably has better wind, I can only report on what it's like now. Has been ridable every day for the last week, although it's a bit on and off. Most of the locals fly Ozones, 9 or 11m. They deal with the gusty conditions well.
As for accommodation, If you're only there for one week just stay at a bigger resort and pay the $40us per night. If not, just rock up and stay one night for $15us on the far side of the road, then hire a bike in the morning and scope out where you want to stay from there. The only time you'd struggle to find a room would be Mid Dec to end Jan (Northern Hemisphere hols).