So I don't confuse you further with YT "statistics" I will answer your questions regarding marking, neutering and anesthesia safety.
Marking is a very difficult thing to correct once he begins and neutering will help with this issue. Yes, this is because their hormones are removed during the neuter. I think this is something that you should speak to your vet about if this is a concern. Personally, 2 of my 3 were neutered/spayed by 6 months and my vet was not concerned so I was not either. They both had any retained teeth removed and he said they were at the end of teething. So this was not an issue either or a need to wait longer.
As for the actual procedure, there is such a very small risk from anesthesia which is way over blown by people that do not understand the OR or what goes on during surgery. I've working in the human OR for many years now and I can assure you that people are not dropping dead on the table like it's played up in our minds from both TV or stories told on line. Having a simple neuter is very safe and with recovery afterward is also pretty quick. Within a day or so he will be back to his old playful self
Anesthesia is metabolized (removed/cleared) by the liver which is one of the reasons that your vet will offer pre-op blood work. They like to know that your puppy has a healthy liver that will allow him to get rid of the anesthesia when he wakes up after his procedure. There are several drugs that your vet uses before, during and after to put his patient to sleep. Afterward, he might be a little sleepy in recovery but that is only because his liver is clearing the anesthesia as he wakes up. Most vets allow the dog to go home that night and when they do it's not uncommon for them just to want to sleep.
I hope that I've been able to reduce your worries over having a neuter as well as answered your questions. My suggestion is always to have a very open conversation with your vet to help alleviate your concerns. Now that things like growth plates and retained teeth were previously brought up I think you should ask your vet to weigh in on their opinion instead of causing yourself further worry and confusion over this subject. Believe me they are more than willing to answer your questions to bring your anxiety down when it comes to your puppy's health.
Good luck and try not to stress yourself out over a procedure that's been done successfully millions of times and on a daily basis for the health of our pets