1) You need to source a stud remover/extractor from an auto parts or tool supply store. 2) The crank sprocket is held on by the harmonic balancer (crank pulley) and two washers (convex side towards the timing belt. The sprocket has a woodruff key (small half moon shaped piece) to stop it from spinning. I t fits in a slot in both the crankshaft and the sprocket. You need to replace it if you can't find it. 3) Depending on how many threads are damaged and how much of the fastener is still in the block, you may need a tap and a screw extractor.
