Unfortunately, Perl is only available if you jump to Illuminated or Premium.
PHP is also WIDELY used on our servers - we can't enable Perl and remove PHP on the Prime Membership, or we'd pretty much destroy the hosting since PHP is what is the driving force behind vBulletin, IPB, MyBB, PHPBB, SMF, Wordpress, Joomla, Mambo, E107, PHPNuke, multiple Radio softwares, multiple shopping cart systems, etc. I'm not saying perl isn't useful, however given PHP's widespread use on the server, there's pretty much no chance we would be able to remove PHP and still run a business.
We do not give out specifications about the servers we have, nor about how many users we have on each.
Illuminated server does have better hardware then the basic free hosting servers, it is very similar in setup to those of our premium hosting.
Number of users on illuminated server will be more then on premium, but less then the basic free servers. As for domains, you can see this for comparison on how many domains each account would be allowed: http://x10hosting.com/free-hosting-comparison