Variables and scripts can be useful depending on the type of storygame you want to create, but they are not essential. The main priority should always be ensuring that your storygame is well written. If you like to plot your stories, plan it out and see if these things are necessary and work from there.
As for previewing your storygames, click 'My Stuff' and go to 'Storygames'. Then just click the title of the storygame you want to preview and it should look like any other published game (aside from the details you are yet to have filled out). You don't have to turn on sneak preview since that just determines whether other members can see your unpublished story.
Hope that helps :)
Strangely enough, although two of your unpublished storygames are on sneak preview, I can only seem to access the 'Testee' one (by going to your profile and selecting the game with the site extension). 'A Dragon's Life' seems to lead to the main storygames page instead. If you did click 'storygames' under 'my stuff' (as opposed to just clicking storygames), you should be able to see a page like this: link
There's also the possibility that it's a glitch or site issue. In that case, if no one else responds here, you could add this problem to this forum.