*MOST* of your basic questions should be answered in the FAQ -
http://www.simviation.com/cgi-bin/yabb2/YaBB.pl?num=1080894097While I've heard of peoaple that are trying to write Python scripts to convert Blender models to the FS-X requirements, I don't think they've come too far.
*At this time* you would export your blender model to a 3DS file, and presuming it maintains the textures and animations, you would import into gmax, and export as to FS-X.
You need to install gmax.
You need to run the SDK installation from teh FS-X Deluxe disc 1, and copy the FS-X gmax gamepack to the correct folder.
You need to download and install the latest FS-X SDK SP1a from the fsinsider.com site (note that you first need to have installed the SDK from the FS-X Deluxe disc.
Then you have to manually create the different folder hierarchies and files comprising an aircraft container".
Install the SDKs, and the documentation pretty much starts you off.