ещё раз = once again / one more time Снова = again
a more thorough explanation :) https://forum.duolingo.com/comment/11690774/Снова-опять-вновь-ещё-раз
I guess this is what you ask https://www.russlandjournal.de/en/learn-russian/russian-alphabet/
Yes, but we actually say "Nós estamos em casa de novo" or just "Estamos em casa de novo", which is more usual on common speech
As for why to use "em casa" instead of "na casa", "em casa" means at home, while "na casa" means in the house, but for this to work there has to be a house of which you were talking about, so the person you're talking to knows what house is "the house"