You can write the chapter as long as you want; whatever feels comfortable to you but, in my opinion and so you won't bore/frustrate readers, a chapter could be between 10 to 15 or 25 pages.

I like the chapter separated PDF files as there are presently.
it is somehow easier to read,and I like getting the surprise each time ^^
(kind of like watching a TV show...you can't wait to find out what happens next and thus look forward to enjoying the next chapter )

I prefer to be able to download the PDF, the format just feels better, but it's your own choice really. With how long your stuff is though, it can be tedious to scroll around a webpage.

Length is your own choice. Do NOT let conventional standards dictate what you define as a chapter or book. In the end, we'd just have less to read more often, which honestly doesn't make it any better than before. In fact, I'd argue that since your stories are generally more immersive, I prefer being forced to sit down and really sink into the text for an hour, making longer better.