chooks4life - THANK YOU SO MUCH! I appreciate the time you put into this, and the quality of the information.
You're most welcome. 
This will be really helpful as I try to develop a socially well-adjusted, self-sustaining flock. The one cockerel I had (that accidentally came with an all-pullet order) started displaying some of these undesirable signs when he was 16 weeks old, but I really didn't know what I was supposed to look for. He would look up at me, drop a wing and try to circle me. I didn't know what that meant, but it made me really uncomfortable. It seemed like an early sign of inappropriate, semi-aggressive behavior and I culled him.
You seem to be making the right decisions and nipping bad traits in the bud. The less tolerance you have for them, the less you and your flock has to suffer.
Prior to this, he had relentlessly chased and harassed the pullets, although he hadn't tried to mount them.
Yep, that does sound bully-ish indeed.
I suppose I should have picked up on his earlier behavior (chasing the females) as a warning sign.
Well, generally yes, but when you first take animals from a background and breeding system that encourages and selects for negative social traits, you can expect to take a while to breed out bad behaviors. I would expect the male to begin showing behavioral improvements in his manners towards hens etc within his first year, or cull him.
If you really like the male, go for it, but otherwise it's worth holding out for a decent rooster to start with. However this cockerel you mention was showing multiple negative traits so it was right to cull him, in my opinion. Over-enthusiasm with the females is one thing, threatening you is another thing entirely. Also, just chasing without attempting to mount --- I would expect such a male to be one that in future scalps and gouges your hens or otherwise attacks them, it does sound abnormal.
I used to be far more tolerant of the 'teenage' behavior of cockerels with hens until I saw it become an accelerating trend of abusing hens in future generations bred from those same males, and began culling against it.
Lots of people practice keeping all males and females gender-segregated for most of their juvenile lives and even most of their adult lives, and males from such a background are often prone to chasing, since they are bred from generations of males that are deprived of normal social interactions with females (normally that includes 'wooing' behaviors, like tidbitting with actual food (not faking), finding nests, etc, gaining the female's trust before attempting to mate) --- and then suddenly put in with a pen of females that are also deprived of social interactions that would set them up to be willing to mate.
What ensues is an abbreviated and rather aggressive version of what's normal. They skip the building of the normal bond and go straight to trying to mate, and from the female's point of view, a strange and aggressive chook has just entered their territory and is charging them and attacking them. It really is set up for distressing relations, and once you repeat that for enough generations you can end up with males and females that have no concept of normal relations. It's been made worse by the notion that males that don't charge and attack females are not 'virile' with this being followed by the culling against males that treat hens kindly and try to build bonds before attempting mating.
Some think that because they mate despite the aggressive approach, it's normal, but a rooster will also respond the same to another rooster or even a hen that aggressively charges and mounts him and 'treads' his back and wings rapidly. He'll complain but automatically get into position and mate like he's a hen. It's an automatic reaction for most chooks regardless of gender.
Many chooks have bi-sexual attraction because of gender segregation, it's normal enough for roosters to mate with roosters and hens with hens, which only fosters more aggression between and among genders since the hierarchies are no longer separate in their minds.
I had one hen that fought with, and beat, 7 brothers (same age as her) one after the other after the other, and every time she beat one, she jumped on him and mated him like a rooster on a hen. Then the next brother would come running, drawn by the fracas, and she'd repeat it with him, fighting then mating, and so forth. Strange behavior but pretty eye-opening about how automatic the mating response to being mounted is, in many chooks. More instinctive chooks will more often react with flat-out refusal to mate, though.
Sounds like my best bet is to have a broody hen raise chicks, and carefully watch for inappropriate behavior. Many folks have recommended carrying aggressive roosters around with them an hour a day to assert dominance, but I was hoping and praying there was a more natural way to get a good rooster - that is - by selecting for it through a combination of breeding, observations and culling.
There definitely is a far greater genetic aspect to it than anything you really do to them, and you can only get good roosters if you won't tolerate bad ones. Breed what you want to see, temperament wise. There will always be the occasional exception to the rule, a good seed from a bad seed and vice versa, but in my experience it's actually quite rare indeed.
Putting up with troublemakers and nasty animals makes it incredibly hard if not impossible to get the happy flock one would hope for.
I originally did try everything to make my bad roosters good, but it became abundantly obvious that managing their bad behavior must be ongoing for their entire lives, and not only that --- the same bad traits were present in their sons and grandsons and great-grandsons.
I made the choice to begin culling against bad traits (rather than devoting time to managing them) one day while actually carrying around a grandson of a bad rooster, 'retraining' him, thinking of how much time I've spent trying to change their nasty mindsets without permanent success, and thinking how much lifetime was I willing to devote to repeating such an apparently fruitless behavior... I didn't want to spend any significant part of my future days repeating this with every generation, wasting time on wastes of space when better roosters could so easily replace them.
It wasn't an easy decision to make the first time but I've never regretted it and my flock still benefits from it.
Best wishes.
