Going for the older models of Prado, Surf or TLC, you run the risk of running into body changed vehicles. Some say body changed vehicles are legal if the body tax is paid, others do not agree. Since fortuner is relatively a newer vehicle, so probability of running into such a vehicle is lowered.
The previous generation of Fortuner earned a bad reputation due to a 2.7L Petrol engine mated to a full time 4wd transmission. People complained about vehicle being under-powered, and to compensate for that, they would drive with a heavy foot. Both of this factors lead to lower fuel efficiency.
Diesel and petrol both variants have their own pros and cons. Keeping other things constant (transmission, type of tyres, vehicle weight) diesel would be more fuel efficient than a petrol engine.A diesel engine is built to last a lifetime, and can take a beating if maintained properly. Petrol engines on the other hand provide quicker acceleration, relatively easier / cheaper maintenance.
I'd recommend buying something within 4.5m and keep the extra 5k for occasional upgrades. A set of decent All-Terrains cost a bloody 100k.
Oh, Surf is a 5 seater by the way - not 7 seater.