1. This can easy be done per script

2. Even Hl² don´t uses as half as much polys as this model has, the game will very slow (I think / 5000 Polys have the best perfomance if I remember correct)

3. The bone animation in A6 works well and you can make very good anims, but I´m a programmer, no artist

4. Never heard of CAL3d and I think there´s no native support, but you could write an exporter

5. The A6 is a good and solid engine. With some tweaks you can have very good graphics, you can use the easy c-script languale or C++ and you have a complete developing suite - what more? It depends on your skills

All in all: if you are good in c++ - use your skills (take a look at this: http://www.rakkarsoft.com/raknet/forum/index.php?topic=765.0) or use Irrlicht) if not (or you just haven´t time to build your own tools) use the A6 - it´s a great engine