ProSite, WHMCS Provisioning, Stripe and SSL

I need some professional advice before I even start with this. How should I setup SSL? I have:

– Cpanel with multisite installation

– CPanel with WHMCS with WHMCS Provisioning

– Both of the above on the same Dedicated IP

I only need SSL on multisite for credit card charging purposes (Stripe, ProSite), and only for the checkout page on multisite. And for WHMCS, well I am not sure, but I think for whole WHMCS.