Ouch, first bump...!
I've connected the bone hierarchy, and added a skin modifier to the mesh. As soon as I add a bone, the mesh becomes lots of times smaller, about the size of a single bone, compared to the mesh. It just resizes itself and moves down under the model, a bit over the B:model_root and all the other dummys, and they're not connected to the model or the bones in any way yet. If I remove the bone, it doesn't change back, but I've ctrl-Z-ed my way back.
I've tried resetting the X-form, checking the pivot point, all fine, before adding the skin modifier. This happens with any bone, and all of the bones I add. It could seem like it's going back to a previous size I had, before scaling my model up to fit the proportions of the swoop I imported and stole tags and dummys from. Any ideas?