Having worked in car rental, but not behind the desks, I would advise people to 1) Check the size of the car you're renting ( 4 BIG people plus 4 BIG suitcases ARE NOT going to fit in a Nissan Micra) and 2) use the car rental co's own site for everything because it seems other sites promise you the sun,moon,and stars, but when you reach the rental desk in the airport it turns out that things you thought were included are not and so begins the lengthy process of deciding if you want what the desk agent is trying to sell you. I could be wrong, but if you have your booking reference off the company's own site then you're thru the process in no time.
Another thing about driving on the 'wrong'/left side of the road - EVERY time you return to your rental car to drive off, WAIT for another car to go by first in the direction you want to go, then follow that car just so you don't come to a bend in the road on the wrong side of the road - crashes can ruin your holiday (if you're 'lucky') or your life !! (and NO, the pedals on right-hand-drive cars are NOT the other way round - I was asked that question more than a few times !) , and don't forget to thoroughly check your rental for any scratches BEFORE leaving the rental depot - it could cost you when you return it !