Before you buy a single chick, spend twenty minutes checking two things: your city's ordinance and your HOA covenant if you have one. Oklahoma has no statewide rule on backyard chickens, so the actual answer depends entirely on where you live. Some cities allow six hens with no permit, some require a permit and a setback, and at least one major city currently bans them outright. Check your city page before you spend a dollar on gear.
What you actually need before chicks arrive
A brooder (a large plastic tote or stock tank works fine to start), a heat source, chick starter feed, a waterer sized for chicks, and pine shavings for bedding. You do not need the full coop built on day one. Chicks live indoors in the brooder for their first several weeks and only move outside once they're feathered out and the weather cooperates.
Chicks vs. started pullets
Day-old chicks are cheaper and give you more breed selection, but they need six to eight weeks of brooding before they can handle outdoor Oklahoma weather, hot or cold. Started pullets cost more but skip the riskiest part of the process, which can be worth it for a first-time keeper.
The first 30 days
Expect the brooder temperature to start around 95°F in the first week and drop about five degrees each week after. Oklahoma's swings between a warm afternoon and a cold night make a simple thermometer in the brooder more useful than a fixed schedule. Watch the chicks, not just the calendar. Chicks huddled tightly under the heat source are cold; chicks spread out panting are too hot.
What it actually costs
Budget more for the brooder setup and starter feed than people expect, and remember the coop itself is usually the single biggest cost in the whole project. It's worth pricing out a coop before committing to chicks so there's no gap between when they outgrow the brooder and when they have somewhere to go.