If you are completely new to sewing, I don't recommend tackling Rose Quartz. You would be working with some more advanced fabrics and techniques. (I've actually been working on a Rose dress with/for a friend of mine [I'm going to be her Pearl], but we're doing it a little differently from canon, so I'll give a more canon response than what I've been doing.)
That said. Here's the simplified breakdown.
Her dress has a lot of translucency to it, and it flows. I would use a sheer material like chiffon that would get you that drape. The cut of her skirt is circle-based.
For the dress, you're going to need to add some structure to it. The bodice will need some structure, likely in the form of boning, for it to stay up with that strapless cut. Be sure it is well-fitted through the torso, under the bust. I would use princess seams in the bodice. The skirt will require some sort of petticoats in order to keep it poofed out like that.
It would be best to leave some type of fabric in the star cutout. I would use a reverse applique so you get the cutout look, but so that the cutout is sturdy because it has other fabric underneath. It'll also make it possible to attach the gem permanently. I would use a mesh fabric that matches your skin tone so it blends in. For attaching the gem, I've used (for Rainbow Quartz, so similar placement) a rhinestone glue
applied to the back of the gem, with a piece of fabric on the underside (against your skin) to catch the glue as it seeps through the mesh and hold it all in place. I haven't tested this at an all-day con yet, but I know the glue I used is sturdy, and it seems to be holding up well.
For the feet, you can make barefoot shoes
, wear shoes that match your skintone, or wear shoes that match the outfit and her personality. Honestly, flats that match your skin as close as possible are probably your best bet, since they will be safer and more comfortable than barefoot shoes and blend in better than clear shoes. (Besides, her dress is long enough that you won't see your feet most of the time.)
It is difficult to dye wigs pink, especially if you are trying to match. If you want more volume than one wig will get you, you should buy multiple wigs and weft them together.
As for your wrist, I don't think anyone will really care. If it's something that bothers you and you want to cover, make something appropriate to the character, but that's entirely up to you.
For the weapons, don't let your own height or size get in the way! If you want the weapons, and especially if you want to look more intimidating or battle-ready, go for it.
If you have more questions, since this is pretty much just a basic breakdown/description of the outfit, just ask. :]