Those sentences sound fine to me, if your clothes are loose enough to move because of the wind. The words "flapping" and "waving" don't have to be used for a particular strength of wind, but flapping seems like a stronger word than waving. Like, a flag waves in the wind, but if it starts flapping around, then it's probably a strong wind haha.

Neither are really correct if you are wearing the clothes. You could say “your clothes are waving because of the light wind”

I pictured the clothes were hanging outside on a clothesline and drying in the wind. Thus they were waving or flapping. It didn't occur to me from these sentences that someone was wearing the clothes.

I would say : the clothes are flapping in the wind. The word strong would be dropped because it would be obvious that the wind was strong if the clothes were flapping in the wind

Not really. In speech we could say His clothes were flapping in the wind. His clothes were flapping in a strong wind. Flags wave, not clothes. ‘The strong wind’ is odd in your sentence because if we know that the wind is strong there wouldn’t usually be a need to repeat it. If the wind hasn’t been referenced, we would use ‘a’.