Allow visitors to click a button (a heart icon) on the post to indicate that they like it. The heart icon should change from black and white outline to red.
The ultimate purpose of this is for visitors to be able to indicate to me which posts they enjoyed the most.
Does anybody have suggestions or advice for me?
Not a heart icon, but similar functionality is possible with the Applause button. You can check out this guide on how to integrate it into a Ghost theme.
If you want visitors to be able to mark their favorites just for themselves, you can store this on the user’s device with a cookie. (Dashi does this, for example.) If you want to track overall ‘likes’, that’s not something Ghost does natively, and you’d need to use a third party solution. (Writing one is on my todo list, but my todo list is really long with things that actually pay money, so…)