Can I do this if I'm not a strong hiker?

Possibly. Ranger's choice means difficulty varies—easy rim walk or strenuous descent. You won't know until departure. Be honest with the ranger; they may offer guidance.

How cold does it get, and what should I wear?

Night temps drop 30–40 degrees. Expect 20–50°F depending on season. Wear layers, insulation, windproof jacket, hat, gloves. Hypothermia is a real risk in winter.

Is it safe to hike in the dark?

Yes, with discipline. Full moon provides substantial light. Your eyes adjust. Red-light flashlights help without destroying night vision. Stay grouped, follow the ranger. Main risk is trip/fall on rocky terrain, not darkness.