So happy to hear in your message the love you have for Murray. That is the most important ingredient for a well adjusted Bully. After that comes calm assertive and consistent training. I am no expert but some of the things you mention are not unusual. I have Miss Tallulah who is now just over a year and baby Buster who is 14 weeks. Personally I think 4 hours may be a bit long right now. The usual rule of thumb I have been taught is for every month of age you can add an hour. But this is just a generalization.
The divider in the crate is good. Generally puppies will not go where they sleep. But I don't think I understand what you mean by puppy pad? I have a big sheepskin pad in Buster's crate. You might want to provide something safe to chew to keep him occupied until he falls asleep. I put in a kong stuffed with Banana. He sucks at it until he falls asleep.
I am a firm believer in only potty training outside. It is too confusing otherwise. I treat Buster every time he goes potty outside and give tons of excited praise. If he has an accident inside ( he hasn't now for 2 weeks) I quietly clean it up. No treat no praise. I also take him out according to the accepted schedule -after waking, after playing, as soon as he wakes after a sleep, after eating etc. he does not have enough insight into his own signals quite yet. Although yesterday he stood by the door, I took him out and he had a huge pee and poop. So there is some progress.
Bullies respond very well to positive reinforcement training. Lots of literature and videos to look at. Murray has a habit that needs to be broken. It is giving him some sort of reward to poop in his crate so you need to offer a better reward for going outside to poop.
Read lots on bite inhibition. That is what you want to teach Murray. They have evil shark teeth and explore everything with their mouth. With Miss Tallulah I was shredded. With Buster not so much because Tallulah is teaching him bite inhibition by correcting him. So grateful for that. Management is best. Put him away in his crate with a treat to calm or redirect his behaviour. When puppies get anxious or over tired they really amp up the biting. When he gets to be too much you need to slow his energy. When Buster starts to mouth and bite I redirect by placing a chew toy in his mouth. Consistency is key.
Tallulah still does not like her harness . When I put it on I jackpot treat her so she lets me get it on without a fuss. She looks so depressed until we get outside and then she forgets about it because there are lots of interesting things to see and smell. With Buster i tried something different. i slowly introduced the harness with tiny treats of kibble and eventually placed it on him without doing it up and and he is now always associating the harness with yummy treats. So far he does not seem to mind it. I am trying to be more patient with him than i was with Miss T. Live and learn.
When T and i went out for walks at the beginning I used very high value treats ( dried liver her absolute favourite) and a random schedule of reinforcement. Not now - but I used to give her a tiny treat every minutes or so. Now just a couple of times on our walk. She loose leash walks and our walks are a wonderful bonding time and a real pleasure. I took a course on walking your dog when she was a pup and this is what i learned . it was invaluable.
Apologies for being so long winded and I know there will be others who have even more wisdom, insight and experience to help you through this wonderful, frustrating, magical time called puppyhood. Would not trade it for anything! Good luck and happy training!!!