If you want your chickens to be used to being handled, it's best to start with chicks. Also you can let them get used to YOUR schedule rather than their hatcheries schedule. Of course there is always the worry of not all the chicks surviving and sexing is always debatable. Oh and you would have to build or buy a brooder. (Not that hard but costs more money) The pullets might not have been handled but it all depends on where you would get them from. Hope this helped!! Good luck!!
Hello and Welcome To BYC! Looks like it is time for chickens! X2 There are +/- to both, for sure chicks are really cute and fun to have and they tend to grow into tamer chickens if you work with them from the beginning, and you can often find chicks of breeds you can't find as older birds, but they are a lot more work and are more delicate and need a brooder to start with ...
With older birds, they don't tend to be as tame since they usually have not been treated like pets, but on the other hand getting eggs four or five months sooner with older birds is really nice, if you work with them, especially bribing them with food, they usually do come around and and become friendly.... You might check what is available in your area, check/post in your state thread https://www.backyardchickens.com/t/270925/find-your-states-thread and look at the BST forum if anything is available in your area that sounds like what you want www.backyardchickens.com/f/67/buy-sell-trade
Cute little coop! I am a fan of getting chicks. You can bond much easier with them by working with them as babies. You also know their history. Where as started bird are more work to tame and you don't always know where they have been or conditions they were kept in. But older birds will start laying quicker. Chicks can die on you too. So it is really up to you and what you think you can handle.
Good luck with this decision but I am sure either chicks or started birds will really enjoy this little coop! Welcome to our flock!