Would this work on a wrought iron bed that has been painted white?

I used it on a black wrought iron headboard and it looks great.

Can it be used on gold plated faucets

Absolutely you can use it on gold faucet. I used it on my faucet which originally had been gold. I have the silver leaf which made the faucet color a bright. shiny nickel. I'm not crazy about the color so going to order pewter and try that. The coverage, ease of use and quality is 5 stars. I'm ready to try this on everything in the house !!! Love it

Would this product work to change a fireplace glass door frame from shiny brass to a brushed/antiqued brass look?

Cover the glass part with cardboard and tape and get spray paint for heated items like headers on a car at auto store or barbque . spray any color you want. They probably havr primed one too to use first .

Can this be used outdoors?

I don't know. I would test a small area first. I would think the weather would dull or ruin finish after a while so I would suggest a sealer of some sort.