That sucks
I would definately let the tank sit without adding anything to it... I know it's boring but you allready know what happens when you add more fish
Give it some time, think about it, and....staring into a tank just full of corals ain't so bad - I have a nano with just corals and it's still pretty interesting!
Of course you know the best thing to do it QT but barring that, yeah, see if you can wait it out - I'd give it at lreast 6 or 8 weeks and hopefully it was only something affecting the clowns and the firsfish can tough it out. (Hopefully he isn't a carrier!!)
Sorry for your loss but try not to get discouraged!
This hobby can be just as rewarding as it is frustrating.
edit: in time you could think about adding inverts for movement, some of the shrimps can be quite comical and add a lot of interest to the tank without being affected by the same parasites as the fish.