the installation script mandates that configuration.php and templates_c/ be chmod'ed to 0777. this is too harsh and not required in some environments, as well as insecure. Some environments only require 06xx or 066x for files and 07xx or 077x for directories.
Instead of requiring that exact permission value, the installation script could instead test files/dirs with is_writable() and friends.
Is my impression correct that WHMCS doesn't support checking domain availability using registrar's reseller API, such as Enom API's Check command?
(I've tried to search this on the forums.)