Guinea pigs like food. They like their hay and their pellets. If you give them veggies from the fridge, that will be a pig trigger for them. Some of them like attention, pets, screeches, and a wide variety of things. I had one guinea pig that loved to cuddle and would make that little chirping noise when I cuddled and rubbed behind her ears, and then I couldn't even pick up the other one. She'd run away from me. So they have very different personalities across the board.

It is super normal. A lot of Guinea pigs are very vocal, and they have a wide variety of sounds they make depending on if they're happy or sad.

Sometimes they mistake you for food if you cut up some veggies, things like that, but in general, it means that they don't like whatever you're doing, so stop.

They can bite. Hopefully, if you socialize them well enough, they won't, but if you startle them or they're not well socialized and not used to something, they can bite.

They can be. Many guinea pigs are friendly and enjoy scratches, but it depends on how well socialized they are.