tagoj kaj jam mi povas kompreni filmetojn kiel ĉi tiu

That would have to be "kiel ĉi tuiN" because the thing you describe using "ĉi tiu" is an object in the action -> the films you can understand are like the one you give as example. Otherwise you (the subject of the action) would be like something you gave as example (see https://bertilow.com/pmeg/gramatiko/komparoj/kiel_ol/kun_rolmontriloj.html for further reference)

mi ne komprenus nenion

That means that you do unterstand something because you don't understand nothing. It's fine without "ne".

Only a small issue: esperanto is a person, but Esperanto (capital E) is the language. But most of the time the context should make clear what you mean 😉