That description almost makes it sound as if you can only have as many documents open as you can find space on the screen for at once.

No. You can have many documents (I don't know how many, the biggest ammount I opened was about 60) open and only one be visible. With that splitscreen, you can also see and edit two different parts of the same file (e.g. a subroutine call in the upper window and its implementation in the lower window or the like)

x) another nice feature I forgot: it can run in a terminal (e.g. ssh or telnet) and as GUI

x) If you don't have root privileges, but may access a c compiler, you can easily compile and install and execute(!) emacs to your homedirectory