Congratulations! Chickens are awesome and more people should keep them.

I have answered this question a few times in the past over at the place with the subs. Bellow is a pretty long wall of text, of what I can remember, in a somewhat prioritized order.

• Chicken math! Always build for twice the bird you’re planning on getting.
• Find a reliable source of bird health info before it’s needed. Vetting something you’ve googled, while in a bit of a panic, and your bird is suffering, sucks.
• Have a plan for treating an injured bird. Most vets won’t treat a chicken, so treating may include culling. Figure out how you will be doing that, and have your method of choice ready. Personally we will hold the chicken with the non-dominant arm and whack it in the back of the head with a piece of steel pipe, before applying a designated, and very sharp, ax to the neck.
• You may be planning on feeding your birds kitchen scrap. At least we were. But scraps will seldom be enough feed, and it will never be the right composition of nutrients. So shop around for feed. There may be a difference in quality, quantity and price. Quality is hard to evaluate, but euros/kg is easy and so is the desired quantity. Shopping around meant that we shaved 6% of the feed cost, 15km off of the round trip, and got the feed in 15kg bags, which fit our 15kg feeder, compared to the 20kg bags we used to buy which didn’t fit and then had to be stored open.
• By now you should have the coop ready, but how about feed storage? It needs to be stored dry and preferably close to where it’s needed.
• Do you have a source of bedding material? If not, then the same thing applies as for feed vis-a-vis both acquisition and storage.
• In my hemisphere winter is coming presently, and thus darkness. Darkness means fewer eggs. We counter this by having battery powered christmas lights (white LEDs that doesn’t blink, they’re not party birds) strung around inside the coop.
• Speaking of winter, it appears that chickens can’t drink solid water - if that’s a possibility where you’re at, then plan ahead. We have dug a hole in the run, where we put a long burning grave candle with an old pot on top. That way the water doesn’t freeze over and also doesn’t heat up to unsanitary temperatures.