First i would advice against using "The Dog Whisperer" as reference material(Episodes itself have warning that you should not try things from them at home, and Cesar have mixed opinions, and methods he came up with himself). Also "pack behavior" is not really true (at least to my knowing and from what I've read), so there is no 'alpha', and dog is not trying to be your boss. for example: https://vcahospitals.com/know-your-pet/dog-behavior-and-training-dominance-alpha-and-pack-leadership-what-does-it-really-mean
I would suggest reading into Positive training methods and watching videos on youtube. One of that kind of channel is made by Zak George, and in my opinion has really good advises and tips about how to deal with dogs.
Link to his channel: https://www.youtube.com/channel/UCZzFRKsgVMhGTxffpzgTJlQ
While keeping dog in crate (big enough crate) in itself is not something bad, but 8h+ can be to much for young dog.
You wrote that you play/walk a lot, that's good thing, what about training? You wrote in one of comments that he's halfway through intermediate training, but how much you train with him outside of what's there. For example, I have 3,5 month border puppy, we're in middle of puppy kindergarten (really basic training, and socialization), but what's there is very limited. We teach him a lot at home (he knows around 12 tricks, and around half of them he can do only with Frisbee gesture, no voice command). From what i know, border collies, need a lot of mental stimulation because of how intelligent they are. Another example: my puppy learned that growling(playful growling) with toy in mouth is his signal "I wanna play", and keeps switching toys until he finds one that will get me play with him (and he knows names of 3 of his toys). I'm yet to know the potential in learning of 7 month border, but you sure can get really creative with teaching him.
But back to issue, if dog is fine when you are with him, and not when you are not, perhaps he is scared, and because of that he tries to drive others away from him by growing, and barking. The idea I have using positive training is to get him understand that other people are fine, even if you are not here, but since issue of him growling/barking already occurred you need to take really small steps to show him that.
1) First thing to do is ready treats, something that your dog loves, maybe it's boiled chicken or something similar? Make it something that you can split into pieces not bigger then pea.
2) You need to start really small, If dog is really fine if you are near, i would go for either walking near family members/housemates, and give him reward every time you walk past someone or you can sit with your dog, and have someone sit/be near dog. The point is to give the dog idea, that others = treat = something good, so you can be creative and do something else, but make it as easy for dog as possible
3) Time to take step, but again it should not be too big. Tell him to stay(if he knows command to just lay peacefully it will be even better) near someone else, make step back, and give him treat
4) Continue on distance if dog is fine, pays attention to you, and doesn't mind someone around him( you can make person move around him a little, so it's not just static post standing). Then you move to next room so your dog can't see you for a brief moment, and back to him to give him reward. If dog is fine wherever you are in house be it near or far from him, you can change room, to going outside
5) Once you start going outside increase moments you are there.
Each time the dog shows signs of discomfort, take step back.
I'm not including giving treats from others, as they can be busy and not have time to help you. But you still can make training of it by making dog be near them (unless that will bother them), but if they have time to help, they sure can help and give treats to dog. And remember, first should be "yes" and then treat when dog does something good, but you probably know this already
Those steps are just idea i had, if you have a way you should also try to find what makes dog growl, because it can be being scared as i said, but it also can be border herding instincts or even something else. The trainer you going to should also be a great help with this issue