I would keep them separated as much as possible at first. certainly never leave Jack alone ever with any child (I would say that about any dog).
Only allow strictly supervised interaction with Jack on a leash held by someone else. The more more you control the situation the better.
You can't allow Jack to become too jealous, but he has to realize the child is above him in the pack order. Fawning all over your son in front of Jack won't help. Our dogs get jealous when we show attention to our teenage daughter- usually what they do is seek bad attention and will up that till they get your attention. Bad attention is better than no attention at all.
it's going to be important to give Jack a lot of special attention.
I would crate jack during feedings and really keep the Jack away from the baby if you are alone. Feed the baby before Jack.
Don't give Jack the chance to do something you will regret. Jack needs to earn his time with your child, showing you he can behave himself around the baby. Same with room privilages.
I'm sure after a proper length of time Jack will bond with you new son.
Be forewarned, our dogs have bitten both our kids. The kids will learn to respect the dog. While totally unacceptable, the bites were never really bad and seemed to be more of them telling the child back off. Every dog is different and maybe it will not happen to you, but the real issue will be when your son becomes a toddler and really can't control his impulses. This is when you really need to watch both like a hawk. A basenji will only tolerate so much slapping & tugging.
Some dogs view a running toddler as wounded prey, so letting the two go out back & run together could be a very bad idea.
I'm sure everything will go fine, but you need to be very vigilant, and learn to expect the unexpected. Don't give Jack a chance to do something bad and you minimize the chances. Likewise children can become very jealous of the dog and like wise seek bad attention or be mean to the dog, provoking the dog, to get him in trouble. "You love that dog more than you love me!"
My wife & I have heard that line many times!
Take one day at a time and all should be fine.