Angels are delicate and I would wait until your tank was set up for at least 4 to 6 months before introducing a angel of any kind into your tank.Tangs get pretty big and are not usually recommended for a 55 gallon.
I'v got a few tanks.I'v got 2 yellow tangs,a blue tang,a pair of ocselaris clowns,a chevron tang, a huma trigger, a panther grouper, a lunar wrasse, a coral beauty, a eiblis angel and a snowflake moray.I'm setting up another tank and looking into a achilles tang and a golden angel.