I am assuming you are applying to grad school, if not, I don't think these answers would apply.
1. Yes, include it! Just have the name of the poster session (ex: Psychology Department Poster Sessions, Honors Poster Session)
2. Def. include it - like someone else said, just say it is (In preparation)
3. I would try to include it everything you have done - data entry, data collection, recruiting participants, literature reviews, etc.
If you look at school websites, a lot of grad students have their CVs poster, and it can be good examples of what it should look like at the end. Feel free to PM me your CV if you want edits - I have spent quite a bit of time working on mine and had several people look over it. I am sure other posters would be happy to help as well.