The corset:

Velvets are flimsy and slippery to work with. I recommend flat-lining your fabric with cotton (or whatever you prefer) to stiffen the fabric. I literally just spray-glue the back side of the fabric and lay it down on the lining fabric, thereafter treating the fabrics as one.
My seam allowances are stitched down to form channels for the boning, and the rest of the channels are created with single-fold bias tape. The top and bottom edges are also finished with single-fold bias tape, hand stitched to the inside. I opted for a side zipper - which won't change your seam allowance, but just be sure not to close up both side seams. Also, you won't want to put boning against the zipper, but I do have boning on both sides of the eyelets in back.


If you have a hard time finding black shoulder pads, just cover white ones with black fabric.
The hardest part is attaching the blouse to the corset - you'll definitely need a person or a dress form to get it lined up all the way around. I pinned mine together about every 3" inches, then I hand-sewed it together from the inside along the top edge of the corset - right into the bias tape.
The overlay:

Like the blouse, it will be easier to line it up if it's on a person or dress form. I apply it with a simple running stitch by hand all around the edge. You could also secure it with a few discreet dabs of fabric glue - careful not to let the glue bleed through other layers below.
The 9-patch rhinestone buttons are fairly easy to find, but the 6-pointed stars and black-leaf sequins continue to elude me. The rest of the rhinestones I just apply with Jewel-glue.