If I write a story on here, than I need to make chapters and posts, but I don't really have those when I write. I've never written anything too long (by my standards), but how do I know how long the post would be compared to paper? (I am not going to count my words as I write them. that is a punishment teachers give students.) On a regular piece of lined paper, with normal sized handwriting and minimal crossing out, about how long would one page be?
Also, when I write, there are times when a break would fit nicely, but other times when I'm on a roll it could go on for a while. So would I have to just cut if in half and leave a cliff hanger, or post it all while the post before and after would be smaller? And what are good ways to end a post?
I haven't actually started writing what I want yet, but I plan to write it on paper, and after about five pages, try to see how long a page is on here. However, I would like to know some estimates before starting.

Just write however long you want. Chapter length is usually measured off words as pages are imprecise. I would recommend no less than 1,000 words a chapter or you're not giving too much to readers. The average seems to be about 3,000 - I personally write up to 10,000 at the most for a chapter. Depending on the font size, an A4 page (handwritten) usually contains about 300-400 words, so you can use that as a rough estimate. Keep in mind rough estimate, because you can fit over a thousand or less than three hundred depending on font size, spacing and amount of corrections.

I think a "page" on RRL is about 400-500 words, which is about the amount of typeface that can be fit into an A5 page (but that's just an estimate).

But really, make chapters however long you want them to. The definition of a chapter is a "division of a book", and as the author you have complete control over how your book is divided. If you start worrying too much about whether your readers will hate what you're doing, step back and think about what you want.

A page on RRL is exactly 275 words. It's I believe the standard of paperback format, which means that the length will roughly correspond to the length of the printed book.