I'll be growing them out in a 60 gal first.
As with other comm tanks - was thinking of some monos or silver dollars as dithers too.
It will be great if you can get some pics or a video of your friend's piranha comm. That will be an amazing scene definitely.
If you have a lot of dithers i would just grow them out together if they are that close in size.....just be ready to replace dithers
Wolves, atf, and pygos?........hahah....nice....my 3 main comm tanks will be almost the same.....pygos, characins (atf), and PBass