Can anyone advise whether this sounds feasible and where I can find car rental in Hiroshima with English GPS.Looking at your itinerary, I don't see the point of traveling by car. Public transportation along the route is very efficient, more comfortable and possibly cheaper. Renting a car, in my opinion, only makes sense if you visit rural areas with bad public transportation or in some special situations, e.g. a large group of travelers or excessive luggage.
It is possible, though.
As for an rental car with English GPS, I don't think it exists. I have never heard of one.