I've rerad up on how other remote ingitions work, and the norm seems either a timer, or a brake sensor. if the brake is depressed, the arduino shuts off the relays, obviously, you put the key in and switch on first.
I'm teaching myself Eagle cad, as theres a PCB company up the road from me who has a 1 day turn around time 
I'm having a hard time learning Eagle, and there arn't many tutorials out there.
But should have my head wrapped around it soon enough