Sounds like your Pup is in charge already!
When my boy was tiny he learnt very quickly going toilet outside means he can get back inside quickly. You don’t want to teach your basenji, whining and biting gets what he wants, he does this and you take him back inside. You are in trouble! .
Bathing is a forever battle with my Basenji a 11kg Basenji suddenly turns into a 450kg Basenji with arms waving and grabbing onto everything near him to avoid the tub. If his paws are dirty use a sponge and water to clean him off. I’ve never had to wash my boy.
When he gets annoyed when you don’t give a treat what do you do?
Your training sessions might be too long; if it’s Repetitive and the same thing you ask him each time he’s getting bored.
He is taking advantage of you, what stimulating games are you playing with him. Do sent work with him he is a scent hound he will love to work with his noise.
And what do you mean by physical play, that could be contributed to the biting.
How old is he aswell?