I can’t really help with such a volume of information, but at least I’ll try to pave the way for a more competent person with these questions for you, Hsiegle :
– do you have backups, of the files, and of the database, done recently, when the website was still working
– Is it the current stable wordpress version, had you just updated it maybe
– can you please try to visit your blog’s file with a FTP client like filezilla, go to (root folder)/wp-content/themes/ and rename (for instance adding an underscore) your current template’s folder, this will make wordress go back to default theme, it may help
– did you change or did you allow a plugin to change the contents of your (root folder)/.htaccess file ? If you want to compare, ask Google for the contents of a wordpress htaccess file ??