2) How do I create a new block and ensure that it is editable by the
site owner? I've seen mention a few times that I should to to
"administer > blocks > add block" but I don't see this option in my site
admin; the closest thing to it is "administer > site building > blocks",
but this page does not include an "add block" function.
It really should have an add block function. There should be two options at the top - "List" and "Add block". What theme is your backend admin area using? If you are using a custom theme, it is possible that it isn't printing out $tabs as it should.
William