1. With all editions
2. Yes, it has ModelED - but making models in a extern modeller is easyer
3. Yes - With hightmaps and direct modelling (with magnet tool/ vertrices tool)
4. ^^ Polygonal/Bounding Box/Spherical Box/ User defined Bounding Box
5. Yes there are good templates, but the c-script language is easy to learn
Yes, the A6 is very easy, stable, has a great workflow and there are serveral plugins around. With them you can have e.g graphiks like in farcry or doom3 or newton game dynamics provides a free physics engine and so on...