There is legislation that decides what you can conjure and what you can not. Because things that you conjure out of thin air will not last, it is illegal in the wizarding world.
The characters in the portraits are not actually ghosts. They mainly are there just to repeat common phrases or serve as a general representation of the individual they depict. A portrait of his parents would not be of much help to Harry.
Because Harry's grandparents were not able to do magic. This is generally frowned upon by those who consider themselves pure, such as the Malfoy's or other antagonists.
No! It has been revealed that there are actually 11 long established and prestigious schools around the globe. These include Castelobruxo in the rainforest of Brazil, Durmstrang Institute (whereas nobody is certain of it’s whereabouts), and Ilvermorny, right here in the United States.
Harry and Hermione are at the Ministry: he ends up leading the Auror department. Ron helps George at the joke shop and does very well. Ginny becomes a professional Quidditch player and then sportswriter for the Daily Prophet.