I need silver (not sure if I'll be using fondant or BC yet) and I can't seem to find it. All I found was dust. What do you all use for silver?

You can mix the silver lustre dust with vodka, lemon extract or clear vanilla and paint it on or use Lucks silver airbrush color. The paint will be more intense and 'jewelry-like', whereas the Lucks is more like a silver glaze or shimmer. HTH

Will the dust be sufficient enough for the Wilton half ball (R2D2's head)?

Luster will get you a shimmery finish and Highlighter will give you more of a crome finish. The dust does go along way.

I find I like dry brushing it onto fresh fondant better then wet painting it on. test it out to see what you like. Roll out a little fondant and do half one way and half the other. see which one you like best.

I like silver Amerimist a lot better than Wilton's silver dust. If you look in my photos, the Thor's Hammer cake was done with Wilton's silver dust over gray fondant. The A monogram on the wedding cake was done with Americolor silver paint (I don't have an airbrush so I put it on with a paintbrush) over white fondant.

I found Bakery Crafts Silver Glaze at a local shop. It worked wonderfully on some cookie details. I'll be using it on fondant for this weekend.

I hated the glaze and I will never use it again. I found it to be like a clear nail polish with glitter in it and the silver would not settle in an even layer. And forget touchups! It's like messing with tacky nailpolish that just gunks up and gets ruined. Haha I have marked on it with a red sharpi...HATE, just so I won't go buying it again.

Like Texas_Rose mentioned, the airbrush colours would work great. Just make sure you have a really nice soft brush.