Halo 5: Guardians has clans, but that’s not what they’re called. They are “Spartan Companies.”
You can start your own group and recruit up to 99 others, or join an existing one. Either way. Each company has private forums, as well as stat tracking for individual members. Best of all, you can design your company’s emblem and write a custom motto. That should be fun.
By creating or joining an active Spartan Company (with a minimum of four members), you’ll be awarded a free REQ pack containing customization items for your character.
Something to set up while you wait for that day-one update to download, perhaps.