when someone asks these questions, there is usually a positive or negative response, i.e. the person is fine or not doing so well. For example . "How are you doing - I am fine! thank you."/ "is everything ok? - NO , i had some problems today with my girlfriend" For the last one, yes it is okay to reply "you too" BUT it would some more respectful if you said "Thank you, you too" , you can also say "Thank you"/"Thanks" and other things that you will learn.