Rather than clicking the plus to add a person, I think a more intuitive action would be to double-click empty space. Whether or not you change that, the 'click + to add a person' doesn't work - when you put the word 'click' on a page, people will click that and not pay attention to the rest of the directions. Even if they did, it's a little confusing because 'click + to add a person' isn't clear. You need to be more specific. 'click the plus button to add a person' and then have the plus button move so people see it.
A simple guided tutorial, similar to the beginning of most mobile games, could help here. You literally walk the user through the process of adding one person (themself most likely) and then let them grow from there. With a 'skip' option of course, if they don't want or need their hand held.
