What are your goals when you hatch? When you hatch are you OK with mixed breed chickens or do you want them to all be be SLW's? Are you going to be raising them for meat, size and early maturity might be a goal. If you will sell the chicks it might be easier if they are all SLW instead of mixed. As best you can (it will not be easy) you need to pick the one(s) that best meet your goals.
I suggest people keep as few males as they can and still meet their goals. That's not because you are guaranteed problems with more roosters but because problems are more likely the more roosters you keep or you may have to work harder to keep them. Since you plan to hatch you will need at least one. A lot of the chicks you hatch will be male, what will you do with them?
How much room do you have? The more room you have the more likely you can keep multiple roosters together. The tighter the space the more likely you will have problems, some serious. The ideal situation for multiple roosters is that they can get far enough away from each other that they can't see each other. Some people do successfully keep multiple roosters in less space but there are more risks. I do not believe in magic ratios for the number of hens for each rooster. Experience has taught me better. You can have the same problems with a high or low ratio.
Another option to keeping more roosters, especially if space is tight, is to create a bachelor pad. Keeping the males separated from the females gives them a lot less to fight about. It is a common solution. While there are ways to keep multiple roosters and without knowing how much room you have or your goals I'd think keeping one may be the right choice for you. Certainly no more than two.
Because of the social interaction in the flock it is challenging to to choose which cockerel is the one that best matches your goals if behaviors are involved. The dominant male suppressed the behaviors of the less dominant so you cannot see their true nature. The competition from the other males can affect him too. A male may act totally differently toward the females and maybe even you and your family if he is promoted to the head rooster position by removing the other males.
Another challenge is that while they are immature the hormones are usually in charge. The cockerels can get pretty wild. The pullets are immature also and don't know how to play their part. Generally when they both mature things settle down quite a bit but it can get petty wild until they do mature. Sometimes the adolescent phase isn't too bad, especially if you have a lot of room, but sometimes it is really wild. Looking at that photo you should be seeing some effects of adolescence by now.
On the other hand it is possible for a chicken to flip when they mature. It is really rare for a female to do that but it's possible. She may become a brute toward other hens. Males are more likely to do that. Again it is kind of rare for a male to become a brute toward the hens as they all mature, usually they mellow out. But his position as flock protector can change him from being a gentle non-threatening rooster toward humans to becoming human aggressive. There are several different theories on how you should or should not treat a cockerel as he is maturing to avoid this potential problem, I have some opinions of my own. Sometimes they work, sometimes they don't.
I tend to select the larger earlier maturing cockerels to keep, but I raise them for meat. In my opinion the early maturing ones tend to have the personality to win over the females by his magnificence and self-confidence. The ones with less self-confidence tend to rely more on brute force to show their dominance over the hens. I also think the more insecure are more likely to become human aggressive just because they are more nervous. I have eaten some early maturing large cockerels because I thought they were too aggressive or brutal. It's not always a clear cut decision. Sometimes I get it wrong.
None of this always holds true, you can find plenty of exceptions to anything I said. About the only think consistent about chickens and their behaviors is their inconsistency. In my opinion picking a cockerel based on behaviors is a crap shoot, both because of the social interactions with other males and females plus he just hasn't matured yet. In your case the pullets haven't matured either.
I think your best bet is to decide on your goals for the cockerel(s) and any chicks that hatch and base your decision on that. You won't really know how well you chose for another 6 months or a year.
Good luck, it can be a stressful decision. I struggle with it.
