In perculas and other clowns the female is generally bigger and bossier.
In the water column the average goby isn't bothered by other fish as it tends to be a bottom dweller and rarely ventures far off the bottom. More than one goby can sometimes be a problem unless you have a larger tank for different territories. Clowns tend to be pretty docile but will show aggressiveness for the "alpha" spot unless trumped by a bigger/more aggressive fish. Coral beautys' don't really fall into that category.
Anytime you add something to your tank it should be quarantined for some time.... but I don't think that is practiced as much as it should be by most aquarists
... guilty as charged here...
The best tried and true method to add ANYTHING to your tank is a drip method.... I use a small syringe and slowly add water while floating the bag...anything I add usually takes about 1-3 hours.
As for feeding, I use a small cup, about a quarter to half cube of frozen gunk and some water from the tank to thaw it out... I use a syringe and long rigid airline tube for target feeding and the remainder is just dumped in to incite a feeding frenzy.