1. There are no threads involved with the headset on a threadless semi-integrated headset which is what the skyhawk frames use. You can either get funky with some welding like you say, or just get a cheap fork with a 1 1/8" steerer. I'd opt for getting a fork, something like this can be had cheap: http://www.amazon.com/FORK-MTB-UNI-H...rds=26%22+fork
2. Pretty much.
Maybe take some pics of what you've got for donor bikes and we can offer up some better tips?