As long as you buy another false perc you should be fine. I would not recommend mixing types at all. Also, I would not say it is going to be a 100% success that they will get along, but there is a chance...I would just look for one larger than the one that is left in the tank. Depending on how big they are I also would not worry too much about the flame angel as my clowns are pretty tough when my coral beauty tries anything funny and will stick up for themselves...