Funny, I got into learning Japanese for the same reason as you - love of films and wanting to understand the original language, even when English subs are available.
It’s far from an easy journey, for me anyway, so I’m probably not best positioned to give advice 
But I wanted to ask:
What kind of films are we talking about?
There’s a big difference between the language spoken in 2025 and in… say, 1955 (to pick a year from the golden age of Japanese cinema). Or between the language of a film by Kore-eda and one by Ozu, to put it in different terms.
It would seem the older ones are difficult even for natives - not so much in understanding, but in reproducing the speech patterns used back then 
Also, do you plan to use Japanese subtitles or none at all?
The answer here would indicate where you should focus your efforts.
Aaaand… let’s prop up the film watching thread we’ve got going here, we’d love to hear what you and anyone else may be watching, with or without English subs 