> there is one process owned by root, and the user for the others is actually "apache"
The question of the owner of the Apache process is answered: It is the user called "apache".
> When attempting to su - apache the response is "This account is currently not available"
That is possible, depending on how that user is configured. See /etc/passwd and /etc/shadow for details.
The question is, why do you want to be "apache"? To give him the ownership of a directory tree? That won't work for a second reason: A user cannot grab ownership, the super user has to give the ownership. See the chown command.
> I came across the fact that apache was the user when I was trying my original trial-and-error cron setup.
I repeat, you can not trail and error in Unix, that is the Windows world.
> If I can't become apache what might my options be?
See "chown" above.
> I also still don't know the path to PHP. My cron is running with just "PHP" as the path.
If cron is happy with just php, then it is in that users $PATH. If you want to get the full path explicitly try "which".
I'm sorry, that I can not give cut-and-paste solutions. You are trying to adapt Debian instrucitons to EC2, which looks like RedHat. That is doable and a stimulating exercise, but you need an understanding of the few Unix commands we have been using sofar, they are not just Mantras.
The first chapter of any popular book on Unix has these things explained.