I agree with @Egghead_Jr on this one. I would get a bird over 1 year old that has been proven. Boys of the same age mature a little faster and are way hornier than the girls. They then grab the girls and make them scream while they rub vents together, since roosters do not have penises . The girls are NEVER happy about this, and have NO say in the matter! A rooster should be more gentile and less amorous than a young cockerel.
I don't think roosters equal that great of protection. And the cost of feeding one (for me $3/month) I could by 12 chicks each year. Of course it would be nice to have a broody raise them. But also, I am guessing we are talking hatchery stock, which is OK but their genetics often don't conform to the SOP for their breed. Which is OK if it fits your plan. Since I want my flock to self sustain for many generations I am trying to get the best genetic start I can. But what would you do with all the extra cockerels you hatch? We will be eating ours.
And from a personal stand point, I like to see different breeds dotting my yard with eye candy. Plus it makes me feel like a kid again when I get to be surprised by what I am going to find in the nest everyday. I like to be able to tell my birds apart at a glance so if I see something wrong I don't have to try to figure out which one it was. And being able to tell the eggs apart can also tell me things about their health like who's laying how often and any deformities. And then there is chicken math!
Breed interest can change. If you are stuck with too many light sussex maybe you won't get a chance to experience so many other wonderful breeds.
We eat our eggs and most are fertilized for sure. There is no difference. An untrained person wouldn't be able to tell at all assuming there hasn't been incubation taken place for a significant amount of time, probably a few days. And if you collect daily, shouldn't have much problem with broodies doing that.
Most of my flock would be much happier without a cockerel to pester them non stop. A rooster should be better. I have 2 sets of pure bred, French Black Copper Marans for dark eggs and meat quality. And Swedish Flower for a dual purpose interesting breed. I also have just egg layers of different breeds, but won't be hatching their eggs on purpose even though they are being bred by my boys and I will probably let them brood if they choose to.
Honestly, I wouldn't have roosters if I didn't have a very specific goal. I do think they are beautiful and I love to hear them crow, though some are more shrill and annoying than others. 3 pullets is not enough for 1 cockerel. But 3 hens and 1 rooster may be OK. As much as I would like to agree that there is a magic # to keep the girls from being over bred... with plenty of girls around I saw 1 pullet get mated by the same cockerel 4 times in less than an hour one day. More hens does give more opportunity to spread the love around. but some just won't give it up and he may not like others.
And my boy pecks down the girls who won't give it up and doesn't let them pass on the roost. To me, it's extra drama. It can be managed though.
Also if you have small kids or dogs, the boys may go after them if they are running around enjoying themselves.
It is a very multifaceted issue. And everybody has different experiences to share. No one way is right, except the way that works for YOU!
If this is your fist year with chickens, I HIGHLY suggest you do not try to add the dynamics of a cock bird at least until your next year.
Another consideration is that layer feed has too much calcium for roosters, especially since you wan't him to live a good long life. It can cause kidney issues long term. So I would feed a flock raiser or grower type feed that has more protein (like 20%) and less calcium (1% is good) and offer oyster shell free choice on the side for layers. Actually the same is true for chicks! Layer won't support growing chicks and it's too difficult for most people to provide multiple feeds plus making them eat the right one. Starter, Raiser, or Grower should be fine for everybody as long as OS is on the side for layers.
Best wishes!