If I write a story based on a movie that's R-Rated, should I use a lot of curse words?

You should use your judgement. If the cursing is attached to the character eg. If the character is really expressive, then don't completely take out all the curses. I think it's always better not to have characters curse because more people will respect the story that way, but if the character curses a lot in the movie you shouldn't ignore it.

If you want more people to watch your series I reccomend you not use that many curses  - but if your charecter gets hurt/sad/angry those are appropriate times to curse, not if your in a random conversation. If you use a curse like every 10 seconds,  I personally wouldn't watch it :/.

Hope this advise is helpful.