I don't have much to offer but since you are asking for any input…
We got our Ella from a breeder at just over 6 months (she is about 15 months now) and we found out later that she had pretty much ZERO socialization with humans other than the breeder herself during that time. She spent almost all her time in a fenced yard with a bunch of other dogs. (And the breeder defended this behavior, but that is another story). She did continue to live with her parents and one sibling. As a result, she is pretty good around other dogs, but exhibits some of the troublesome behavior that you mentioned around humans.
I sometimes sense that Ella is just not as happy as she could be. She definitely seemed "lost" for many months when we got her as far as figuring out what to do and what was expected of her. Much slower than most other dogs. She would shiver and shake with nervousness often. Sometimes I also thought she might not be quite right in the head. I don't think that as much anymore. Although she eventually did bond pretty well to us she is skittish around most other people. She will cuddle next to us (nap time and sleep time are the best) but she is just as likely to get herself comfortable by herself in another part of the room. She was not food motivated at all when we got her and still only moderately food motivated.
Regarding food, we found that adding a little water and heating up the food did make a big difference. Also, we changed her food from what the breeder was giving her and she has been much more excited about the new food that we switched to months ago. Also, we only feed her AFTER walks. She is more excited about food after a walk. I forget what her old food was but it was not very high quality. We switched to Innova Evo. She likes the chicken and the beef.
It took us months before we could even begin any obedience training but now she is really coming along learning commands. While these commands are very useful in themselves, I think it stimulates the dogs brain, builds the connection between you and the dog and establishes your leadership. A good trainer in 2 sessions gave us the guidance we needed to get Ella learning 6 or 8 new commands. It might be worth a try. Made me realize Ella was smarter than I gave her credit. Ella is a huge chewer and loves her chew toys, which we have plenty. She gets a very happy and contented expression on her face when she is chewing so we let her.
We have no other pets or children, so it is possible that Ella landed in the best situation possible with us.
You seem committed to making it work. The one thing that has kept me going with Ella is that while she has a long way to go in a lot of ways, she seems to be making progress as opposed to getting worse. That being said, she can back-slide and has on several occasions. She is independent, sometimes aloof, sometimes demanding, always exasperating. Somehow, I have accepted that this is the Basenji way.
Good luck.