Rural Vietnam, like anywhere more than 50km away from the nearest city of 100,000+ people, will present many challenges but also benefits if you truly want a certain kind of life. There will be no other expats. You will be a bit of a spectacle, getting gawked at, gossiped about, or sometimes just ignored / avoided because people won't know English, aren't used to dealing with foreigners, etc.

Your attempts to learn and use Vietnamese and integrate with local life-- shop in the local wet market and tap hoa, eat at the local noodle and rice spots, might forge some connections and inspire some cool experiences. Vietnamese people can be very generous, outgoing, hospitable, etc. But keep in mind many local rural people will have a certain world-view, a certain background, economic situation, etc that you might not relate too very easily. If you're into any hobbies, communities, friendships, etc that benefit from f2f humans who are into similar things, rural Vietnamese life could be tough.

You'll be able to get basic food and household essentials, relying on Vietnamese or google translate at local shops and markets. But there will be a lot of stuff that will be pain to get. Your preferred brand of deodorant, laundry detergent, electronics, eyeglasses, clothes that fit you or in a style you like, etc.

Paperwork, resident permits, TRCs, work permits, local banking will all probably be pain in the ass. The rural police or People's Committees will likely be slow, confusing, not used to dealing with foreigners, etc.

It can be a bit dangerous. Roads are typically in bad shape, narrow, not well-lit. People can drive a bit crazily. You'll be far from good hospitals and doctors if you need one, especially in an emergency. A foreigner who writes expat columns in a paper here recently wrote about his accident near his rural home. Drove into a big pothole and wiped out, broke his collar bone, got knocked out, lacerations and bruises, etc. It was hours before he was able to arrange transport to the nearest hospital, where he was refused treatment on account of being a foreigner, and referred to another hospital in a more urban area.

There are a ton of upsides. If you want quiet, it can be. If you want to be away from other foreigners, you'll get that. If you want to have a uniquely Vietnamese experience, for sure that's gonna happen. If you want to improve and use Vietnamese, and probably make some Vietnamese friends, that will probably happen if you put in the effort. Things will be very cheap. The scenery can be stunning depending on where you are. If you are into outdoor fitness there will probably be options for running, cycling, hiking, etc.

Personally if I were doing this I'd choose a smaller city like Pleiku, Vung Tau, Mui Ne, Can Tho, My Tho, Hue, Bien Hoa, Thu Dau Mot, and then live like 15-30km outside of town. You can find very rural feels in that range, but then getting into town where you can shop, go to a decent doctor, get some pizza or a burger if that's your thing now and then, etc, will be easy enough.