Interesting styling puzzle to be solved.
The dress itself is a.m.a.z.i.n.g.
I wonder why you feel you have to hide the goods. For me, if that is a starting point, you run a chance of being rather self-contentious, which may spoil the fun of the event and the outfit.
I am not keen on options 1-5, even without reading what you want to achieve it looked to me like you're trying to hide behind the necklaces.
Options 6-8 are closer to what I'd choose for what you want to achieve, although I'd go for the shorter necklaces closer to the neck. The ones shown here fall to low, again drawing attention to the goods. With shorter waterfall style necklace you'd achieve the coverage and bring focus to the face.
Funnily, I have a black velvet dress with similar neckline and it originally came with the satin string that was threaded across the lower part of the neckline (it had 3-4 loops on each side of the v-neck) and you could tie it, creating "shoelace" effect - I have no better explanation, but I guess you can picture it? I found it too fussy though and removed the string, sewn in the loops and wore the dress to a couple weddings, once with a pearl choker necklace, another time with short black one that had funky pendant.
ETA: No.8 gave me an idea... you look really great with red lipstick. How about leaving the necklace out altogether and just have fab silver cuff and red shoes??