I was wondering if it acceptable for me to carry photocopies of my passport and so on for the car, instead of my originals ?
No you risk being fined if you dont carry original ID with you.
I have a copy of my passport in the car which has been authenticated by a Notary. I think it cost €8.
My understanding from the Notaries Office is that it is as acceptable as the original. The passport is safely locked away.