La palabra casa es un sustantivo...

femenino o masculino?

Femenino because you say “La casa” not “El casa”.

Feminine because when you use “la” it end with an a making it feminine

if it were to be masculine it would be “el”

to know how to write feminine or masculine look at the word that comes next.
ex: yo no pie do ir a al pizzaria el sabado.
since it ended with o it uses el

Yes it is correct like that is there anything else you need to add ?

For this question, it will be important to use the words "mejor" (better), "lo mejor" (the best), and "lo peor" (the worst). while "mejor" is comparative (you are comparing one thing to something else), "lo mejor" and "lo peor" are superlative (there is nothing else better or worse than what these words are describing - there is no comparison).  you could say something like: la música rap es mejor que la música clásica - que es lo peor - pero la música rock es lo mejor de todas las formas de la música (rap music is better than classical music - which is the worst - but rock music is the best out of all the forms of music).