Sorry if this is duplicate advice, so many great posts in this thread!
If you're planning to hatch your own eggs, think about what you want in the babies you'll hatch.  Size will matter if you plan to eat the extra boys.  If egg color is a factor for you and you have any of the blue/green layers in your mix, look for a cockerel with a pea comb - oftentimes it goes with having the blue egg gene. 
But mostly one that's nice to you, nice to the hens, and meets your own personal criteria.  I just had a 2-3 month old cockerel that started picking fights with the hens.  For a few days it seemed like there were more squabbles going on, but I didn't know who (big area, lots of birds).
Then it became clear when he posted himself by the coop to harass the hens as they went to lay eggs - he forced hens to fight him, and when they'd give up and run, he chased them down and ripped a chunk of feathers out of their backs and kicked them one more time.  While I watched, he did this to 5 hens in under 10 minutes ... so I caught him- and dispatched him on the spot.   A cute black cockerel with a pea comb and crest feathers ... none of which mattered at that point.
They can change dramatically once hormones hit- what they do when it happens dictates their fate in my flock.  Whatever switch flipped in his young brain that said attack and hurt the hens isn't one I want to pass on - and nobody gets to give the girls a bad time.  
There's a difference between learning the act of mating and the inevitable pullet squabbles and screams that will go with it in the beginning.  It's important to watch what's actually going on while everyone figures things out - that can help narrow the field.  Not every roo will be a sweet talking Cassanova - but there's no reason to put up with one who is rough or abusive to the hens.  For mine, aggression towards the hens is an immediate deal breaker.   I keep several adult roosters and usually the cockerels until the 4-5 month range, all with the main flock, and it is peaceful.  Then I decide who is worth keeping, who is worth the effort of rehoming, and who becomes meat.
Getting that first good rooster is the challenge, because he doesn't have an authority figure to learn from.   The other factor is your girls are the same age- if there were older girls, they would lay down the law for that first group of cockerels growing up. 
So, you may want to be prepared to have a separate pen for the guys until the girls start laying as soon as they begin pestering the not-yet-ready pullets.  Some do this and add one rooster at a time to see how he treats them as part of the decision making process.
Welcome!