Colt 1911A1 Field Strip Project???

I am fairly new to the blender game engine (gone through some tutorials) and was wondering if it is even possibly to do what I am trying to do.

I want to use the game engine to make a program that demonstrates and then allows the user to field strip a 1911A1 pistol. I have a few questions off the bat and am not really sure where to start with the actual game programming.

Is there a way to make my model solid (collision) but have the abilty for other objects to pass through holes of that object (having the barrel fit inside the slide, rails on the slide fitting onto the rails on the reciever, etc)???

Also my model is i think 7445 or something polys is that going to be to much for the game engine to handle even though the model will be basically the only thing in the scene??

And one last thing for now is there an easy way to make a spring model that is not an insane amount of polys for the game engine?