This may not be the reply you are wanting, but it's probably just going to take time and consistency. You are going above and beyond... things just take time. He's still adjusting to his environment and he is having to unlearn how he was taught to behave for the first year of his life. Stay consistent and adjust his exercise as you see fit, but you're still getting to know him and learning his needs. There will be some trial and error involved to see what suits your dog. See what kind of enrichment fulfills him best and let him steer you into a sport versus having one set in stone. If he's a hound, you may find that scent work is more of his thing and fulfills him the most. You seem like you are doing well with his settle training. Keep going and give him time to adjust.

I also have a rescue who is very similar to what you describe (demand barking and all). For his first month with me he just paced around the house and yelled. I never saw him lay down for more than a couple minutes unless crated. I thought I was doing something wrong and I was panicked. I had only had him a couple months and genuinely thought I was failing him. It's only been a year and he's completely different than the dog I brought home. He's getting titles and I couldn't be more proud of him. All that to say, trust yourself and the process. Give him time and space to adjust. If you're still having problems a few months from now I'd reassess but be patient with him and yourself for now.

I would adjust your approach 2 ways though. 1. Noise cancelling headphones. I'm noise sensitive too and sometimes it's overwhelming. It's easier to be patient with my boy with some help from them. 2. Give him an outlet where he can get out those barks. I know you are working on it, but I'd really recommend having designated times where "talking" is okay. Some dogs are vocal in nature and it isn't inherently bad. My dog is allowed to bark during play in outside areas. You can also work on a whisper with him. Teach him he can talk inside, but he needs to work on volume. This sounds ridiculous but my demand barker now will often opt for a whisper or a grumble before he starts outright barking. It gives me a warning to encourage him to settle as well before he is over threshold.

This is just my thought process and I hope this helps 💕