>>19028
I guess the 2s signify some footnote. I've no idea.
Maximum files, I think 5 the max.
Max file size is 350MB on paper. But even with JS disabled it's hard to upload a ~300 MB file. I managed couple of times. With JS on don't expect nowhere that. Still even a 100 MB is insanely large compared to other imageboards.
Thread limit is how many threads are allowed. I think 160 max.

>>19030
There is a checkbox above the new images feed on the home page. For displaying NSFW boards (well, all boards really). If it is unchecked for you, then for you it won't show up.