i would wait a month more as is it probably not a good idea until uve got everything under control. that doesnt happen in a month. if u want another tang, it has to be a completely different body shape then the sail fin to reduce aggression (no yellow tang). be aware that tangs grow...and if u dont plan on going bigger tank wise its probably better u stick with just one....they also poop a lot.
and good addition is a decorated goby, u dont see these too often, but they are great u get the best of both work when it comes to gobys. its a "light" sand sifter, so it will not starve case it readily accepts prepared food but ur sand will always be clean, er un less u got cyno. and clown fish, i have 2 Ocellaris (one with stripes one with out

), a pair of them are fun to watch, especially when u have an anemone(that shouldnt come till mush later tho.....much later. i jump the gun and thank god mine is still alive). surf liveaquara for ideas, the have little bios on most fish so u can kinda get an idea on how they behave and what attention they need, it also states the skill level required for the care of that fish.
hope this helps.