Ulysses had some great pointers, a little tongue-in-cheek maybe...
But seriously, unless you are getting a 'steal' for an older 91-95 explorer, I'd shy away. Especially if you are anticipating this to be a primary driver... By now, most explorers of that vintage are going to be high in mileage and unless extremely well cared for, it will be a 'money-pit' (even if it has been well cared for).
I've had a 91 for 120,000 miles, (75,000 - 195,000). Over the years, I've replaced the engine, starter (3 times), Alternator (twice), brakes (fronts every 12,000 to 15,000 miles) RAB bushings (needs them again). Door handles have broken, center console arm rest broke, numerous gauge display problems (see other post). I've avoided the tranny problems (knock on wood). I've also had problems with the heads and gaskets, intake manifold, replaced the radiator, heater core...
The list goes on....
Rick