Logic express and pro compatibility

Hey there. To answer your questions:

1. Yes, but all the instruments/plug-ins that are Logic Pro only, will (obviously) not work in LE.
2. Yes it has.
3. I don't know. Can you tell in which file format they samples come? Or is it a Gigastudio format? If the latter, I think you can't.

Joining in with two short questions !! I want to get Logic to share songs with my bandmate, but we need to be able to open each others files with no problems, so :

1. So by that reasoning, I suppose Pro could open an Express file with even less trouble ?

and

2. What about compatibility between different versions, like Logic 8 and 9 ? Logic 9 could probably open the file from the older version, but is it also true for the opposite ?