I also have some questions regarding the market

I think you may be looking for particular stats (especially for 3) more than personal experiences/opinions. Here are my personal experiences.

I've seen young Vietnamese play football in AstroTurf type grounds and in parks. They also play this game where they form a circle and kick a shuttlecock like object from player to player.

Also seen Vietnamese younger and older gen. play badminton in parks. jogging, walking (particularly older gen.).

I was staying in D7 in HCM, and there was a gym with all modern facilities close to my apt. e.g. weights, threadmills, steamroom, yoga etc..They gave me tour of gym. I used this gym on day membership - no issues.

I've hardly seen any overweight Vietnamese. cannot recall. did see a somewhat overweight guy (early/mid 20's) yesterday dancing. I wouldn't say he was obese. overweight?, probably.

So you are thinking about moving to Vietnam to find a "future partner" and have questions about the "market" of available girls or guys? Sure I will tackle that since I'm an expert.

Health consciousness? The park near me in Bangkok is full of runners in early mornings and evenings. And a loud music thing at 6pm with hundreds of jumping/dancing girls. There are a lot less motorbikes in BKK (I almost never see women driving a motorbike but they use motorbike taxis). Vietnamese will use their motorbike to drive one block, and people seem to walk more in Bangkok. I can't remember anyone walking in Saigon except inside a mall.  I think the Thais win.

There are gyms in Saigon but I can't compare if more or less.

Vietnamese food has a lot more vegetables, and soups, and seafood.
Thai street food doesn't look good to me. Little hot dogs, fried things, waffles, etc. Saigon street food is actual meals. Vietnamese wins.
(Thai food courts are more like Vietnamese street food)

Vietnamese and Thais are all mostly slim, pretty much the same. I think Thais are a few centimeters taller. I wonder about the next generation of Vietnamese though - ever watch a group of school kids walk down the street? like half are overweight. Why do slim parents have chubby kids?

I'm still puzzled about the term "market". Did the OP use the word geographically, or did he mean market as a place to exchange personal enticement commercially?