okay i cant really answer number 2 because i dont know you but i can help with all of the other ones.
question 1: something i found interesting was the black family tree and how sirius really didnt get along with most of his family.
question 2: again sorry cant give you an exact answer because i dont know you but you could say that tonks reminds you of one of your family members with how goofy she is.
question 3: the climax occurs at the ministry with the fight against malfoy sr. and bellatrix and the other death eaters. some members of the DA (dumbledores army) go with harry to the ministry because he saw sirius (his godfather and only piece of family he has left) being tortured by voldemort.
question 4: absolutely. harry potter is amazing and Rowling does a really good job of telling the whole story.
next part question 1: i knew that umbridge was going to be a terrible person from the moment she was brought up.
next part question 2: umbridges description was enough to go on that it just gave you this feeling of just a terrible person and an even worse toad. (because she's described as alike to a toad)
i really hope this helped. :)