Will these fit my deep-dish wheels without hitting the brake caliper?

That's the whole point of the extended spike design — extra length clears deeper offsets. Double-check your specific wheel offset and brake setup before install, but these are built to handle aggressive wheel fitments.

Do these come with a key or locking mechanism?

No — these are standard extended spike nuts. If you need anti-theft lug locks, you'll want to source locking nuts separately and mix them into your set.

Can I reuse my old lug nut seats, or do I need new studs?

These threads are M12x1.5 — a universal size. Your existing studs should work fine as long as they're the same thread pitch. No stud replacement needed unless they're damaged or a different size.