Welcome Sully. Cockerels are a dime a dozen. Get your pullets (female chicken from hatch date to her first birthday) and get them raised up well, preferably to the point of lay before you even consider getting a cockerel (male chicken less than a year old) or a rooster (over a year old).
In order to safely house a roo, you will need EVEN MORE SPACE than the generally recommended 4 s.f./chicken in your coop and 10 s.f./chicken in your run. Be aware that a roo will not so much protect your flock as he will sound the alarm system.
A good roo: keeps his eye out for predators so his ladies can eat in peace. He also dances for his ladies, finds and shares treats, accompanies them to/from the nest, even finds new and novel nesting spaces for them! He takes no for an answer, does not attempt to breed a pullet or hen who is not laying and not receptive. He takes good care of his babies. Most of all, he is not chicken or people aggressive.
The biggest issue of adding a cockerel or roo at a later date is the biosecurity risk. You always run the risk of bringing a "forever" disease into your flock any time you add an older bird.
That being said, the best option for flock harmony would be to add a mature roo to your flock of laying pullets. The good roo would be a proven breeder, one who has a track record of being gentle with his ladies and not people aggressive.
The next option would be to start your flock this season with chicks, then add a few more chicks in the spring, including a cockerel chick. He would grow up in your flock, and be schooled in proper dating etiquette by your hens.
Many of us keep a multi age flock: remove some older birds each year, add some chicks each year. That way you don't end up with a hen house full of old biddies who are no longer paying the rent (with eggs).