Wouldn't you just want to turn it inside out and than fold the cut part and sew it so it wont rip more? I've never done it, but that's what I think you would do.
yea. If there are seams I would say get a seamcutter(thats not the right name, but im drawing a blank) and remove the sleeves that way rather than scissoring them off
what you should really do is cut off the sleeves and make put a zipper on so you can always put the sleeves back on if you want. i cant really explain how to do it, but if you cant figure it out a tailor can do it easily