The Focus is an excellent used car - highly rated. If you've never owned a car before I presume you don't have any no-claims bonus years for an insurance policy. This may not matter if you're over, say, 35, but could make things expensive if you're younger, male and live in a city, especially as this Focus has a 2.0 petrol engine.
This car has average mileage for its age. If you like the look of it and are happy with the insurance quotes you've had (try www.confused.com) there are a few things you need to watch for: look at the car in daylight, not in the dark - this makes it easier to spot scratches and dents; make sure the owner has a V5 registration certificate - this will tell you how many owners it's had and whether the seller at work is the registered keeper; check the service book to see if all the appropriate boxes have been stamped - ie it has a full service history (this is important); look under the bonnet and check the fluid levels seem okay (but don't check the engine coolant if the car's warm!); check tyre depth - there should be plenty of tread left as it's passed it's MoT; get the owner to start the engine while you stand behind - watch the exhaust, there shouldn't be any smoke (smoke would indicate that the engine is burning oil).
Above all, don't feel that you should rush into buying it. There are loads of Focuses out there, many with the excellent TDCi diesel engine and 1.6 Zetec petrol.
And yes, the AA, RAC et al will do inspections. Some also include HPI checks, which let you know if it's ever been an insurance write-off or has outstanding finance on it.