Is it normal to just want to hook-up with someone?

Your feelings are relatively common, but it's not good to just use people for sex. You need to be completely honest with this person, don't lie to get what you want, because that's a shitty thing to do. Liars are shitty people, don't be a shitty person.

Yes, but be careful not to get an STD or worse, and make sure not to make them confused. That will end badly.

Of course it is, I think we all want to do this secretly ;)

I think it's normal, but make sure that she knows you're 'sexually attracted' to them rather than 'romantically attracted'. This has happened to me before and she thought that I really liked her whereas I didn't have romantic feelings for her. So be careful how you talk to her.

Friends with benifits is a thing, but be careful

Have a one nighter with them. It might turn into an ongoing thing. I had a friend of mine who had what I thought was his gf. They were just friends who liked to fuck each other once in a while during a dry spell.

Yes.
Be safe physically and emotionally and enjoy!