Welcome!
It is a lot to learn lol - but in the end, it's only as complicated as you make it. We all built coops and runs and have vitamin protocols and feeding standards and and and....you get the point. But really, chickens are hardy little devils, and my personal opinion is that they have a great easy learning curve. You will have wiggle room for mistakes, so don't be hard on yourself starting out. Some people build practical poultry mansions for them, and I personally know a guy that has chickens living in his junk yard all year round. They find their own shelter there and he really only puts feed out for them in the winter. But most of us here seem to fall somewhere in between those two extremes.
Your major advantage is that you're starting with full grown chickens, so they've already made it through the touch and go phase of their infancy. If you've already got pets, you probably have a crate or a portable kennel lying around somewhere that the birds can use at night to keep them safe. And it sounds like you can range them in your yard until you get something more permanent.
But be careful, the "chicken bug" is about to bite you. You'll find you start watching the birds instead of TV. You'll learn their favorite treats and go out of your way to make sure you have some on hand. It's a vicious cycle.
And pretty soon you'll get to play the favorite BYC game, 'Roo or Pullet'. Now I'm horrible at this game, but it's fun to play. Hope to see you around the forums for some time to come.
And pics of your new birds are always appreciated.