One thing that I notice in your post is that you say you got him at 7wks? That is really young for a Basenji puppy to have been taken from the litter. My pups do not go till they are 10wks old at the earlist. They miss a great deal of socialization with the litter when removed to early, in my opinion.
Second, while I know that it is not usual for people in Europe, I would suggest you think about having him neutered. He is at that "young boy" age, this is now what is considered Basenji breeding season… so you have in addition to other things, hormones at work.
And last I would suggest that he doesn't rightfully know his place in the pack order... but a behaviorist should be able to help you sort that out. Have you talked to his breeders? What are his sire and dam like? How is their temperament?