An adult Naso gets huge. My friend Don has a 15" one in his 300g. It'll take over a month for a new tank to slowly adjust its bacterial culture & other parameters to safely handle the fish you already have.
Like the others stated, enjoy what you have for now & later, maybe add something med. size & peaceful, like a Sohal tang (JJ). These are fabulous fish - beautiful, lots of motion, hardy, but aggressive. If a Sohal is added, you'll have the added advantage of never having to add anymore fish into the tank since the Sohal would kill it anyways.
On the serious side, I just added a bonded pair of Bird Wrasse to my 100g, & love em. Awesome colours & patterns, swims right out front, neat shape & great eaters. However, I'm hoping to eventually upgrade to a +200g.