I'm working on something along these lines right now. If you have a character model that is animated, and then you attach a separate model (say, a sword) to the character via script (using vec_for_vertex) the sword can be made to follow the character, but won't animate with him. You can set its pan, roll, and tilt to be equal to the character, but when it comes to actions like swinging the sword, this won't do.

I haven't done this, but I think your best bet is to animate the character and his sword/armor together in your modelling program, then export them separately. Then when you attach, you can animate them both separately, but they will be synched.

As for your "sleeves" problem, I can not think of an easy solution. You could always keep the sleeves as a separate model from the armor, and it would work, but the number of individual models would get astronomical.