The install.site script will be run at the end of the install after you configured the time zone. Not when you reboot the computer
Ftp is a more environment friendly way to experiment with a customized install then burning an ISO each time. After you figured everything out and everything is working OK from a local ftp server, only then you burn your CD.
I use custom installs by using
bsd.rd and a serial console to log everything. I also use
tee to provide a log of all output produced by the
install.site script.
BTW your tar command is missing the
p option to preserve the permissions. The script needs root ownership and execute permissions.