I would say Harry's favorite place is Hogwarts because it was his first real home.
constellations
If you mean Hogwarts, no one know, except for the fact that it's in Europe.
Hogwarts's (Hogwarts is Harry Potter's school) motto is "Draco Dormiens Nunquam Titillandus" which means "Never tickle a sleeping dragon".
He spent it at Hogwarts.
Severus Snape He had known Lily before they both went to Hogwarts
Dumbledore anonymously returned the Invisibility Cloak to Harry Potter on his first Christmas at Hogwarts.
The death of his parents, his entrance at Hogwarts and his ultimate victory over Lord Voldemort
In his will Dumbledore left Harry the Golden Snitch (that Harry had caught in his first Quidditch match) and the sword of Gryffindor (Deathly Hallows Ch. 7) On Harry's first Christmas at Hogwarts - Dumbledore gave him James Potters Invisibilty Cape (Philosophers Stone Ch. 12)
Nowadays term 'alma mater' doesn't refer to a person, but a school, so it would be Hogwarts.
Yes, along with Ron and Hermiones children, and Draco Malfoy's children.
The "school for magic" in Harry Potter is Hogwarts School of Witchcraft and Wizardry. There are four houses and each one bears the name of the four founders of Hogwarts, respectively: Gryffindor, Hufflepuff, Ravenclaw, and Slytherin.