BF, I would consider Yellow Tangs to be in the "medium" category of difficulty. They are hardy as long as water quality is good, but will NOT tolerate poor husbandry; often the first to show stress and die due to low PH, dissolved organics, poor filtration, etc. They could be considered a canary fish, or system indicator of overall aquarium health. YT's are removed from the Big Island at a rate of about 250,000 or more per year, causing some debate about sustainability. I have always thought they should command a higher price, considering their beauty, but they can still be had for about 15.00-20.00 each.
These fish should be reserved for systems 6 months old or more, which usually warrants some green micro algae for continuous grazing. Algae can also be farmed on rocks placed in grow-out jars located in a sunny window sill with an airstone, then rotated into the display as needed. These living greens can be supplemented with Nori and other processed algae products; YT's are not picky eaters but greens must be part of the diet for optimum health and vigor.