Help on 5 week trip, beginning stages of planning

Hey everyone! I am traveling to Vietnam mid February to mid March 2013, will be in Vietnam for 5 weeks total. This will be my first trip to Asia! Anyways....I've read through my LP guide book and picked out some of the most interesting sounding destinations, however I wanted to get some advice on which locations might be best for me. I will be traveling with my boyfriend, we are both in our early 3o's, prefer budget accommodations, as cheap as we can get as long as it's not a dorm room. I do not like obscenely touristy destinations, for example, even if the city/town itself is a wonderful place, if I'm being constantly hassel-ed or ripped off, I would rather go somewhere more off the beaten track. I understand I'm going to be hassled, but some places are much worse than others, I'm sure you know what I mean :) Anyways...so here's the towns/cities etc. that I think look interesting, any advice would be great, for example, are the places I've picked repetitive? Like too many islands etc? Which national park is best for wildlife? We like beaches, beautiful scenery, good/cheap food, secluded spots, and yes, I know I cannot fit all these places into my trip but I will narrow it down later, thanks!

Mekong-Ben Tre, Tra Vinh, Can Tho, Ca Mau, Phy Quoc Island, Ba Chuc, Chau Doc
Central Highlands-Cat Tien National Park
South Central-Son My, Quy Hoa Beach, Dai Lanh Beach, Nha Tranng, Whale Island, Con Duo Islands
Central-Vinh Moc Tunnels, Khe Sanh Combat Base, Hue, Bach Man National Park, Hoi An, Cham Isls, My Son
North Central-Phong Nha-Ke Bank National Park
Northeast-Ba Be National Park, Halong Bay, Lan Ha Bay or Bai Tu Long Bay? Cat Ba National Park, Cao Bang
FYI, Yes, I'm def going to HCMC and Hanoi!