I think you will enjoy the car a lot, it's one of the great performance bargains of all time, so good luck on your search. The cars have proven to be quite reliable. Mine has low mileage so I can't help you there, but there are plenty of members reporting high mileage and dramatically increased horsepower, with the cars still being quite reliable.
There was a recall on certain '14 and '15 models for a defect in the cylinder head which could cause a coolant leak which could start a fire.The recall didn't replace the head, it just installed a new sensor and a few other parts, so if you do look at models during that time you may want to check and see if they are subject to the recall.
The only other issue which people frequently report is the HVAC blend door actuators can go out and start clicking. There are three of them, two are pretty easy to replace and one doesn't go out much. This issue isn't unique to Fords.
Two things that make me feel good about the reliability of the car are that first, the engines in our cars were or are used virtually stock in Formula Ford. As the video below will show, the car is also able to stand up to the extreme demands of rallying in virtually stock form. This is my favorite video to post for new or perspective members.
View: https://www.youtube.com/watch?v=kM1nkR8pkX4&list=FLur65YQuzud3gXqwZTZTrxQ&index=10