i would wait to let the frogspawn get adjusted to its new environs first before adding the clowns.
as a habit i try to do a water change before adding any corals, i'm sure it doesn't make that much of a difference though as long as your water parameters are very good.
frogspawn is usually considered a moderately difficult species to keep.
i feed my frogspawn by going to the grocery store and buying fresh shrimp (i'm on the gulf coast so i don't know if fresh is available in your area, frozen should be ok too) and cutting a small piece off and placing it on the top of the frogspawn once the lights are out and it has shrunken down to night time size. you may have to hold the shrimp there for a little while to get the FS to accept the food but mine seems to love the shrimp.
as far as acclimating it, i float the bag for a while till the temps equalize then i open the bag and use some sort of clip to hold it to the side of the tank, then i add 1/2 cup of tank water every 5 mins till the bag is full, dump out half the water and do it again, after the bag has been filled with tank water twice then you can set the frogspawn on the tank bottom.
i usually leave a new coral on the bottom of the tank for a week so that it gets used to the lighting in the tank and then place them higher in the rock work, taking time to leave them in middle zone if it is going to go to the top of the tank.
hope that helps, i was where you were a few months ago and found out all this stuff about FS. i want to get another FS and a hammer coral next, i love the euphyllia!