Oh wow -- how fun! I love the paper theme idea. Good luck with the planning and folding!
We made origami invitations -- got really nice white and royal mulberry-type paper from Kim's Crane (http://www.kimscrane.com/
) and also had translucent paper run thru the laser printer. The mulberry paper has pearlish and metallic threads in it and was really pretty and subtle. The square is 12" and folded down to 4.5" x 6.25" -- it fit perfectly into a translucent envelope (from marcospaper.com)
Be forewarned -- it took quite a while to make 150 invites, but they were well worth the time
If there's any interest I'll post a folding tutorial.