What does ChatGPT+ actually do?

Hey there, I have exams in a few weeks and I've been using ChatGPT sometimes to summarize some stuff and write me flash cards to practice. We do have a lot of huge .pdf-files that contain walls of text and ChatGPT was somewhat helpful, though he did sometimes leave parts out. When it comes to maths he also sometimes does make mistakes which is negligible, but still, I heard that the Plus version does help a lot with that as well.

Though I have two important questions about the plus version. First I would like to fully understand the models, like right now I have two versions available, a stronger one, I think ChatGPT 4 or something and a weaker one when I used up to much of my advanced one. I heard that with plus you have access to an even greater version and if that version is used up by your daily limit you have infinite access on my "strongest" one that I can only use for like 40 messages or something.

And my most important question is about the file limit, since right now I can only send him 3 files per day, which is really not cutting it if I want to get through the texts before my exams with ChatGPT, so I was wondering if the Pro version changes anything about your upload-limit as well. Right now I can't even chat further with ChatGPT if I already sent him a file and my limit is up, basically rendering the entire chat useless until I have access to advanced analysis. Sorry in case my English is a bit hard to read, I'm German.

Thanks in advance!