Once I convert my licence to an FAA PPL will I have to do
an IR on a S/E piston or will my A320 IR be sufficient?
If you are doing a 61.75 validation then to add Instrument privilege you will need to sit the IFP Exam and do an IPC.
If you are doing the full FAA PPL then you will need to do the IR exam and checkride.
I can highly recommend Pelican Aviation at North Perry. In fact I will be there end of next week.