Splitting a document in two is usually about a size limit, and it is a better answer than compressing until the text is unreadable.
A document has structure. Splitting between two sections is far more useful to the reader than splitting at page fifty because that happened to be half. If there is a natural break near the middle, use it.
Name the files properly. Part 1 of 2 and Part 2 of 2 in the filename tells the recipient immediately that a second file exists and which to open first. A file called document_2 tells them nothing.
Halving the pages does not always halve the file size, because pages differ. If one half is still over the limit, split that half again rather than compressing everything.
Not necessarily. Image heavy pages weigh far more than text pages.
Yes, save each range as its own file.
No.