Most Car hire companies are based on airport you just collect and return. 
All hire cars are automatic and have A/C. Sat Navs can be hired.
It is best to shop about as not all deals offer a free additional driver.
At the booking in desk the assistant will always ask you to upgrade. This will be an extra cost. Only do this at the airport if you feel the car you booked is not suitable or too small. It is better and cheaper to do this before you go.
You will need a current FULL UK driving licence and a credit card. Check whether you need to return the car will the tank full or empty. The gas/petrol is usually much cheaper outside the airport than through the hire company.

Under 25s may be charged a lot extra - check with the company's details.
Children under 5 must have a boaster seat and infants under 3 a car seat. You can take your own or hire at a charge from car company.