The fourth element to consider is What is the Stake? Your story needs to have a reason to be written. Does this just have meaning to you or does it have a meaning to other people. You want to look at the big picture. There are dozens of plot ideas but you need to figure a way to show what you mean. The easiest way is to look at some of the plot ideas used for years. Love Conquers All is one. So is Crime Doesn't Pay. Just what makes yours have a twist on these and other common ideas.
One way to go about this is to boil your idea down to a sentence or perhaps two. I'm working on a story now that I'll try to do this for. Zach has been burned by a bad marriage and now has custody of his two sons though one is not his biologically. How can he find love when he has no reason to trust women? Now this is a variation on Love Conquers All. but working iwth the story are amny elements that have reasons for love not to be triumphant.
A fantasy I just completed is a bit different for though there are romances in the story, they aren't the true focus. It rather belongs to the Good versus Evil kind of plot. An evil woman sets out to fine the fabled Three of Three promised in an ancient prophecy believing this will allow her to rule the world. What happens when her plans go awry?
This is the sort of thing you should do with your idea and go through the four steps to find if the plot will become a story. Then the time has come to begin writing and revising.