First Explorer - High mileage going to be a problem?

Hi there!

I am shopping my first Explore (finally) but I am not sure about the high
mileage on vehicles that I've found so far, sky-high! I've a very tied budget
for my first car. I just finished university and I got a job far from home, I will
be driving on the highway on a daily basis. Safety is priority to me then. I am
looking for 3th gen, 4L v6 ideally. What should I be checking (besides
transmission and engine light) in an Explore over 280,000km? What about
an 2006/07 model over 300,000km?

I am planning to ride this not more then 1 year though.

Thank you all