1) A waist stay. I have mostly seen it called a petersham in older clothing, though it would still be correct. Interesting FYI (or maybe it's only interesting to sewing-geek me) is that Petersham actually refers to a type of ribbon, and the name became interchangeable with the term waist stay. Both grosgrain and petersham can be used to make waist stays.
2) Not sure that this has a term. It looks like a variation on binding, but it doesn't look like a true bound seam. Binding uses a strip of fabric or tape to encase a raw edge. The strip is first sewn to one side of the raw edge, then it is sewn to the other side, thereby encasing the raw edge.
3) I would call this a tailor's tack, though really a tailor's tack is used for marking points during the construction process and isn't intended to be a permanent tack. There may be an other term, but I can't think of it at the moment...
Laura