I think it's a big ask to have people watch 30 movies in a month. I'm assuming you're thinking a month. I'd like to participate but it's simply too much of my free time to do a movie a day.
There's also the possible issue of whether all of these are available on streaming services as easily as most of the Marvel stuff is.
If it was me, I'd aim for around 12-15 max for a month. Maybe do a month of Westerns, then a month of something else, then go back to Westerns again, etc so that people don't get burnt out.
On the nomination side, I think there's value in having multiple versions of a movie. It's been years since I watched them but I remember both versions of 3:10 to Yuma having a very different vibe to them, to the point where I could appreciate the differences instead of thinking of one as "canonical".
I think it's also would be neat to directly compare the different takes on Wyatt Earp/Doc Holliday/Gunfight at the OK Corral. There's been at least 5 or 6 over the last 60+ years.
3 Months, with possible extensions usually. Like how this project went from November through January.