The verb "estar" show a passing state, to address condition if you are about how something. "La fiesta esta en mi casa" indicates that the party is temporily passing by my house, arrived but it will come. The verb "es" to essential quality if you are talking about what something is. "La fiesta es en mi casa" indicates that the party started and will end in my house.

Well, when you refer to an event happening somewhere you need to use ES : La fiesta ES en mi casa. La cena es en el restaurante. La boda es en noviembre... When you use ES , you describe a characteristic of the subject( in this case "la fiesta") ESTÁ is use for location and also to describe: El libro ESTÁ en la mesa (location) La fiesta ESTÁ muy divertida. La margarita está muy rica. I need to look for the actual grammar reason for this... But this is how it is...

This is a very difficult question to answer but I'll weigh in to see if I can at least help you a bit. I usually tell people that "ser" is for intrinsic qualities while "estar" is for qualities that can change. That's why you can say "Soy feliz" = "I'm a happy person" and "Estoy feliz"="I'm happy (now)". In this case you use "ser" because the party can only be at your house. If you expected the party to move you could phrase it differently. You'll get the hang of "ser" y "estar" eventually.

creo que en este caso se podria suponer que estas hablando del origen de la fiesta no del lugar. Para el español el verbo "To Be" significa ser o estar, como ya sabes.

In english it´s the same, but not in spanish , are completely differents words