I have to make a gold sequin princess cake soon (the cakes that you cover in piping gel & stick confetti sprinkles to then you hand paint the entire thing gold). My questions are... how many 3oz. bottles of the wilton pastel colored confetti sprinkles do you think I should order to cover an entire 8" cake? I've never done this kind of thing before so I have no idea how much I would need. And what do you use to make that high metallic paint (like in the photo below)... gold highlighter dust or something else?
But to try to answer your questions on how much you need. It's hard to say, you didn't mention how tall you were making it. As tall as the cake above? Then perhaps anywhere between 6 to 10 bottles. I would lean towards 10 or more. Better to buy more than you need than not enough.
First and foremost, if the "sequins" will be, or are likely to be, eaten, then absolutely NO HIGHLIGHTER. It is for decoration only and never to be eaten. Actually, luster dusts that are not marked FDA approved & edible are also for decoration only and not to be eaten. Edible, FDA approved dusts are now widely available at thesugarart.com, pristinepowders.com,sugarpaste.com, globalsugarart.com, and others.
For the pastel quins, you can find those in bulk online and they'll be a lot cheaper than multiple bottles of the Wilton's--unless, of course, you have ton of 50% off coupons from somewhere. Here's and example: http://www.amazon.com/gp/product/B008Y2TST0/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687682&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B006ZDGSWA&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0YVYMT7YQ29V9H8CH5FE
Depends on the size of the sequins. The cake pictured above has smaller sequins (1/8") and will take more but if you use the larger ones (1/4") it will take fewer. Definitely buy in bulk or you will spend a fortune in little bottles and I am sure there will be a chance to use the sequins again. I did a 6" x 4" with the 1/4" sprinkles and used a over half of a one pound bag. Be sure to let your piping gel dry before trying to paint the sequins or you will have a big mess. I let my dry overnight. The fan brush works great to get into the difficult spots. It took me quite some time to paint to make sure I had all the little nooks and crannies covered. My cake was for looks only not edible so I didn't have to worry about the dust.