Thats a lot of questions:
-3D max 8 costs money
-Yes it does have a 30 day trial
-The .tga files are located in .pk3 file of base folder (game directory). Use winzip to open the .pk3.
-I'm not sure what you mean, but the model has a hierarchy, limbs are linked together and use a naming convention that cannot be changed...it also uses a tag system to keep track of body parts location when cut off.
-To make a model from scratch, you first learn how to model :P, then you create your character around the JK3 skeleton, next you rig and then hierarchy model parts.
Read the tutorials on my website for more info.