SureAI

Every time now, I've managed to launch the game far enough to show the menu backgroun (without any text on it) and then closes after a couple of seconds

EDIT: forgot to add, I manually added all the files as I'd already created a backup and followed the instructions of an older thread on here to change the launcher's installation status

Tried the manual thing myself, at some point, and the same thing happened to me (no text, crashes etc). The problem is with the manual install; remove everything, do a clean Skyrim install (or revert to your backup, if you think it's stable) and install via the launcher.

Does it matter that my backup has mods in it?

nvm I just deleted all the enderal files from the directory

Please let the launcher install Enderal. Do not unzip the files by yourself.
Here is a great installation guide.