How the hell do you rig clothes on a character without the clothing being 40 feet from the actual model? I get so much clipping.
When it comes to weapons, I've made each one of them have the same bones in the same position. After that, I can take the default bones for all the weapons, animate it along side the player's swing animation, then export the weapon's animation to call upon when the player swings. Everything lines up and looks good, so that may be a possibility for what you need to do. Just make a universal set of bones for all your clothing and animate the movement of the clothing with the character bones. You can just mount the clothing onto the character and line up the origin or roots, so everything lines up properly. When it comes to playing the animations at the same time, you'll have to refer to code.
Just an idea, though. I don't really have any other thoughts on that.