For a thorough overview of Apache's core AllowOverride directive (including options), here's your link: http://httpd.apache.org/docs/2.2/mod/core.html#allowoverride. Basically, it enables (All) or disables (None) use of the .htaccess file, i.e., All is required if you want to use your .htaccess file. I rely on mod_rewrite and change my code often enough that I need to use .htaccess.
You can use your Options +Indexes in the httpd.conf, httpd-vhosts.conf or .htaccess file.
No, if this is your client, then he/she should be able to give you FTP access (username and password to the domain's DocumentRoot directory, i.e., the client's public_html or www directory) even if only on a temporary basis.
As before, IMHO, it's NOT advisable to provide directory listings to the public so FTP is my recommendation. It can be setup quickly and deleted by the client even faster.
I have used a script to read a directory and list files but I removed that script upon completing my task.