We also have mixed fleet 320/321, but our SOP is for F/O to notify ATC of the abort and the Capt to make the PA to remain seated. Capt will then carry out Memory Items eg Offending Master Off, Fire p/b etc. while F/O monitors. All obviously subject to incapacitation requirements. Then a pause - "is it still burning etc?" If Evac required then the F/O reads and does the Emerg Evac list, which includes shutting down the other eng if not already there, while Capt orders the Evac. Our QRH's are specific for A320 or the A321.
The APU is left ON for T/O for the packs - would be turned off as part of the Emerg Evac C/list. As far as I'm aware the C/C have to wait for the order before evac except in certain circumstances (ie if they think we're dead)!