Go read the latest X-Plane Dev Blog post. They are still ironing out bugs and optimizing X-Plane 10 for all the drivers. Be patient, frame rates will improve.
1. I believe that blender comes with its own build of python to run on. 2. I alos believe that blender 2.5 and up uses python 3 not 2. Just my 2 cents.
You shouldn't loose any thing. The only things you lose are new features implemented in 2.5, but that shouldn't be a problem. Unless you have some seriously funky animations.
Marginal's blender export script only supports python 2, which is up to blender 2.49. For python 3 and 2.5 and up there is a script in development at the .org. The exporting of the mesh works fine if you set it up correctly, but there are currently no bone animations (at least not the last time I checked).
Well now this isn't for x-plane, but it is aviation related, and I made it today. Still texturing, Adding details here and there. [EDIT] picture removed.
Not sure i quite understand what you are asking. But for the first question, try 'p', and for the second, hover you cursor over one of the vertices, or what ever selection mode you are in, and press 'l'.