For 1, those instructions were for a specific subset of customers who got a free hosting with domain offer a very long time ago. Almost everyone has been moved from classic hosting to web hosting at this point. If that's the case your plan will be called something like deluxe web hosting linux.
For 2, web hosting is more than enough for most customers. With a few exceptions, you won't get time moved across or a refund if you move between web hosting and cpanel hosting.
For 3, you can install one GoDaddy certificate to web hosting, and it has to be applied to the primary domain. You'd need a UCC that covers the main site and additional ones if you want to cover addon domains. With cPanel, you're free to install certificates from any provider.