Just a few curious cat questions...?

Cats purr when they breathe in and out. They purr all the time, even though you may not know it. This is because they have a flap of skin inside their mouth, which vibrates when they breathe in or out. (wiki.com)

Kittens get milk by nursing from their mother. They press against their mother with one paw and then the other. This is called "kneading". Kneading helps the mother cat give milk to the kittens. When adult cats knead with her paws, it reminds her of her mother when she was a kitten. (breeders-choice.com)

Catnip is a mint-like herb that attracts cats. Some cats do get "high", some don't.

Cats aren't always cleaning themselves. They like their fur to readjust it in order to control their body temperature. Too cold? Lick it that way. Too hot? Lick it the other way.

All theses answers can be found on www.petplace.com

I'm afraid I can only answer question #2. As for the other questions, I really don't have any knowledge.

But regarding why cats knead on soft things -- it's because when they were nursing as kittens, they kneaded on their mother's belly to stimulate milk flow. When they were nursing, they felt very happy and secure because they were close to their mother and their tummies were getting filled. So they learn to associate the action (kneading) with the happy and secure feeling. As they get older, they continue the action so that they can experience that same feeling again.

Hopefully, somebody else can answer your other questions.