Will these fit my current wheels without spacers or adapters?

These are M12 x 1.25 metric — that's the thread size and pitch. If your wheels are drilled for M12 studs with 1.25 pitch spacing, you're good. Verify your stud spec before ordering; a mismatched thread pitch won't seat properly.

Do I need to replace all four wheels' worth of lugs at once?

You don't have to, but it's smart practice to replace a full set or at minimum stick to matching specs across one axle. This set gives you 20 pieces — enough for 5 wheels if you're running a spare, or covers a full four-wheel application with two extras for backups.

Can I paint or polish these after installation?

The anodized finish is sealed and durable as-is. If you want a different color, you'd need to strip the anodize first — sandblasting or chemical stripping — then apply your own finish. Easier route: stick with the green or source a different color from the start.