Ruching/Gathering Help? Sewing Machines Parts and Sales in Los Angeles

I'm self drafting my own prom dress, and I'm trying to make the top look very similar to this, where it is a sweetheart neckline with crossed material that is ruched/gathered. Mine will cross so much that I'll have a cut outish thing at my belly button, like this but obviously with ruching. The problem is I have no experience with draping material and I cannot find any patterns or tutorials on the internet for sweetheart crossed ruching.If anyone knows of a good tutorial or just has any tips of their own I would really appreciate it!! I bought practice material to experiment with and make a "rough draft" that I can then use as pattern pieces for the real thing, and my actual material and practice material is stretchy.