If you want transparency, make an Alpha channel or put the objects on a transparent background in Photoshop. You must save the images in a format that supports transparency such as TIFF.
You import them by clicking the Import Files button or simply drag onto the FCP Browser from the Finder.
2. A regular plug in or an FXPlug plugin?
3. No. Why not use the Contact link on his website and ask the man himself? http://www.lucavisualfx.com/contact.htm