1. Can be done as soon as the Terrain SDK is available.
There´s unfortunately no release date, rumour sais it´s well underway though.
2.&3. Yes. you need the aircraft & vehicle SDK off the
http://microsoftgamesinsider.com/CFSInsider/default.htm?nc=1 site and Gmax from here
http://www.discreet.com/products/gmax/ Beside that you´ll need a lot of time and patient and say goodby to social life and family.
5_1 textures are saved in dds format, a compressed dxt format. you can convert bitmaps to dds using a tool DXTbmp by Martin Wright, available here.
http://www.mnwright.btinternet.co.uk/index.htm5_2. no documentation on this one, you´d need to hack it on your own.
7. Possible. you´d need the FS2002 ATCVoicepackSDK available at
http://zone.msn.com/flightsim/FS02DevDeskSDK00.asp and do some good amount of reading and testing as nobody has ported the method over to CFS3 so far, but generally should it be the same format.
8. As far as the game engine is concerned, see 5_2.
Most of the config files are in xml format, 3d models can be created using the SDK exporter in conjunction with Gmax
9, Yes, refer to the aircraft & vehicles SDK