and that many of them are knocking on your door and disturbing you, especially after dark. You haven't seen anything else so you can't complain about anything else.

They might or might not start keeping an eye on him, depending on the management. Considering there was a shooting in your parking lot, I'd suspect that they will.

and assuming you want to call the cops, then the easiest thing to do is go and find a pay phone, call the police (not 911, since it's not an emergency), and anonymously report that you suspect drug activity is going on at Unit Number Whatever at such-and-such apartment complex. (Since you don't have to be a genius to work out that the only reason some sketchy dude is getting a stream of regular visitors who stay for 5 minutes tops is because he's a dealer. Which could mean he's selling weed, but could also mean he's selling meth or something else.)

1. He woke me up one night at Midnight. He had some kind of electronic equipment he wanted to sell me.
He said he didn’t know what it was, what it did, or how much it was worth ~ but he would sell it to me for $25.
I gave him hell for waking me.

2. He knocked on my door one night at 9 P.M. He said he had 100 pounds of meat he needed to sell.
I told him I wasn’t interested.

I lived above some drug dealers. Go to the police station and make the report there. They should not have to bother you at home after that. These will not be street cops. They will be narcotics squad. In my case, they were invisible for months. Then out of the blue, I received a call from the head of the investigation team. He said they had staked out the house, witnessed drug sales, and tried to buy drugs on several occasions. Although they did not make an arrest, they were made aware of the activity. I also think maybe the drug dealers got spooked (which was a good thing).

In my case there were tiny ziploc bags lying around the yard. I collected some and handed them over to the police. They definitely had been used to hold crack. If you can find something like that to bolster your claim, then they will have to take the investigation seriously.

Go to the area command and ask to talk with someone.
But there's a very murderous gang in the city and if he's tied into them,
I'm a cooked goose.