If you could get a mated pair of bangaii cardinals would be best, they can get a bit cranky with others. Perculas are on the lower end of the aggression scale when it comes to cardinals, be advised that a sexually mature pair will want to keep about 25g as a territory.
I would urge you to research refugiums for pod breeding and the timelines to get one up and running. Mandarins eat constantly during there waking hours and can go through hundreds of pods in a day. If you follow the advice of the algagen folks then I fear your mandarin will slowly starve like so many mandarins. Good luck just my 2 cents.