Bottom line for Perl. Nothing in Moodle. Bottom line for php extensions ... relate to if site is running https:// with a valid cert or not. Cart/Horse ... Apache is the horse pulling the Moodle cart.
Google seems to be on a mission these days to get *everyone* running their sites under https:// ... for good reasons. Read somewhere that they have/plan to have an indicator in search results with some sort of indication of 'site trust' (lack of the actual term).
In the docs for Moodle concerning running a site under SSL (which is really an Apache thang ... on CentOS ... /etc/httpd/conf.d/ssl.conf). As is good advice, the docs say to make sure your apache can respond to ssl *before* switching your Moodle to https ... or lock yourself out of Moodle (temporary and can be fixed ... uhhh, been there and done that 'DUH!' thang.).
As far as version of ssl importance ... yes, DO keep that up to date fixed/patched. Been issues, as of late, with openssl on ALL platforms .... things like 'HeartBleed'. Moodle may not be the attack vector, but is affected by HearBleed then, it follows, that Moodle affected - notice I did NOT say 'infected'. ;)
As far as your OS version ... as long as it's supported. Latest and greatest doesn't always equate to the best. Have found that it's good to be near the 'leading edge' rather than on 'bleeding edge' when it comes to server/service like Moodle - especially for a HS.
'spirit of sharing', Ken