Yes هتلی بزرگ is correct. And about your second question یک فیلم ایرانیی seems wrong. When the adjective ends to ی we can't add another ی to make it indefinite, we can add this ی to the noun in this case. Just like your first question. فیلمی ایرانی is correct. یک فیلم ایرانی is correct too. Both of them are indefinite. Another example: او یک لباس آبی پوشیده بود/او لباسی آبی پوشیده بود But او لباس آبیی پوشیده بود isn't correct.

To make something indefinite, you should either use یک before it or add ی to the end of it, but not both at the same time, except maybe occasionally in colloquial speech, e.g. یک حالِ عجیبی دارم. As an aside, sometimes both the noun and the adjective end with ی, e.g. بیماریِ جدّی. Although using یک before them works perfectly fine here too, there is a way to add another ی in such cases as well, using an additional ا before it, i.e. بیماری‌ای جدّی/بیماریِ جدّی‌ای/یک بیماریِ جدّی.

sorry I "Entered" after lines but sentences are mixed. I rewrite it with a * star to separate them. Here: indefinite= ناشناخته / نکره * But ناشناجته is wrong. * یک هتل بزرگ ,هتل بزرگی, هتلی بزرگ are all correct. * Native speakers also sometimes in their talking say "یک هتل بزرگی" but it's not correct I think. They use it though. * Also natives may say یک فیلم ایرانی‌ای دیدم instead of using رو / را to say: یک فیلم ایرانی رو دیدم/ یک فیلم ایرانی را دیدم. (I'm not sure if it's grammatically correct but we use it in talking)

indefinite= ناشناخته / نکره. ناشناجته is wrong. یک هتل بزرگ ,هتل بزرگی هتلی بزرگ are all correct. Native speakers also sometimes in talking say "یک هتل بزرگی" but it's not correct I think. They use it though. Also natives may say یک فیلم ایرانی‌ای دیدم instead of using رو / را to say: یک فیلم ایرانی رو دیدم/ یک فیلم ایرانی را دیدم. (I'm not sure if it's grammatically correct but we use it in talking)