Hi there, and welcome to BYC!
These are great questions.
Pros of buying chicks:
Chicks are cute.
It gives you time to build a chicken coop.
Greater variety of breeds available.
It's less likely you will import chicken diseases.
Cons of buying chicks:
You need a brooder, and they have to be raised indoors or somewhere warm.
Most breeders have a minimum order of chicks.
No eggs for 16-24 weeks.
Chicks require more care and babysitting.
Laying hens are not as readily available, nor can you get them in as many breeds, as chicks. However, in my county, you can regularly get them at the animal shelter for only 2.00 apiece: these are hens past their laying prime. It's hard to tell how old a chicken is once they are grown.
Introducing new chickens is often quite a chore. the older chickens peck the younger ones.
Most chickens will like you as soon as they figure out where the treats come from, but it's probably safer to raise your own chicks if you are looking for cuddly pets.
My baby chicks hated to be held and did not like me at all, but once they grew a bit and were out of the brooder they got more friendly. Some breeds are friendlier than others: Buff Orpingtons and Silkies are often recommended as pets, but Silkies don't lay well.
Have you decided on what breeds you want?