Any tips of must sees and what to avoid would be great. Will be renting a 110cc scooter and doing a big circle starting in ho chi mein city , going half way in and coming back via train and rest down some of the coast.
Make sure you have travel medical insurance that covers motorcycles, scooters. I used World Nomads and unfortunately can confirm that they were ok with me being on a bike. Make sure you have an IDP, double check, but I think a US IDP is valid in Vietnam, my Canadian IDP was not. Heard that cops are cracking down on foreigners driving without proper licenses, also travel medical is void without a license in the country. I would rent from either Saigon Motorcycles, or Tigit. Most of the local rental places are pretty shady. Be sure to get a decent helmet, you can buy one for a reasonable price from Saigon Motorcycles and other sources, or bring one. For most Vietnamese, a helmet is just a formality to avoid a fine, safety is not a primary concern. Buy/bring rain gear, you'll need it at some point.
Goes without saying, but be careful, especially if you have never ridden in SE Asia. The drivers basically look straight ahead, even when changing lanes, or going through a roundabout. The roads are very far from North American quality, lots of junk, potholes, various spills.
vietnamcoracle.com has an amazingly well detailed guide on moto travel in Vietnam, and what to see, with routes.
Besides all that, have a blast! Vietnam is a really special place.