Honestly, I think that's really smart, to do a summary of map out your story. What's funny for me though is that writing a summary demotivates me. I don't know why. I do usually think about what I'm going to write, but writing a summary KILLS me. I like jsut writing and seeing where it ends up. Is that so bad? =)
Good plan. If you're starting out writing and you don't feel like taking the FanFic Route (which I wouldn't suggest. Waste of time, rather) try out some short stories so you can see how it feels to write prose.
Decide how long you want it to be, and then maybe do a short (two to three paragraph) summary of each 'chapter' so that when you're writing you have something to follow.
Welcome to Mibba! ^^ I'm Nikki, if you ever need help with anything feel free to hit me up! ^^