Our Lela has a lot of pack howl in her musical variations, and LOUD! After a minute her quieter older sister Binti will join in, in a lower key. What we found that helps a lot is this: make good eye contact just before you leave, and tell you will be out and when you will be back. Just as you would to a human. Then make sure you are back at the mentioned time. No howling. When we got this advice from a dog therapist we didn't believe it, but we gave it a shot. It does work.
Go on facebook: there are multiple European groups dedicated to basenji adoptions, like https://www.facebook.com/groups/637260023052459/?ref=bookmarks
Agree with eeeefarm. We have two lovely, laidback sisters, who growl and baroo a lot when meeting other dogs on leash. It takes calmness and practice to teach them to behave themselves. You can dedicate entire walks to addressing this issue. It can be a lot of 'work', but also fun and rewarding to see your B change. And it is wonderful for bonding.
Concur with what's been said already, especially the lying down, or in case of emergency, get their attention and FALL to the ground. They don't like that, and want to know what's up with you. Also, if they go off on their own, they usually return to the place where they last saw you (at least mine do), OR they will pick up my scent on the route that we went and walk back to the car or house (happened multiple times). Still stressful, though.
We feed raw meat (deep frozen) and like that a lot (our 2 sisters do, too!). Some vegetables too, like broccoli, cabbage, red beet, carrot, and the like. Both cooked and raw. We only bath them when they have rolled in something stinking, like a dead bird or so. When wet or muddy, we give them a rub with an old towel - they do the rest.
You can work on it - opening the front door and closing it, without leaving. Then leaving for a minute, then a little more, and so on. What also helps a lot, strange as it may sound, is telling that you are going and when you will be back (make sure you are back at the right time!). Never a problem, for up to 3-4 hours. We don't crate our two sisters - they sleep all day anyway. Good luck!