I haven't used YABB2, but I can answer your other questions. Perl is at /usr/bin/perl, and symlinked from /usr/local/bin/perl, so either path will work. You don't need a cgi-bin directory; files ending in .cgi can be executed from anywhere on your site. If you want to apply the same to .pl files, put the following line in an .htaccess file in the root directory of your site:
AddHandler cgi-script .pl
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