I'm not familiar with your flash, but back in the day we used what were called "auto" flashes. They had a sensor on the front panel which read the light reflected from the subject and quenched the flash when enough had been received for a proper exposure. The sensor typically had a 3 or more position selector, Manual, and 1, two or more positions for the aperture to be set on the camera. The back panel allowed one to set the ASA or ISO of the film and then told you which aperture to set on the lens for the given sensor selector setting. The larger the aperture the greater range offered by the flash. Much easier to use than to describe.
Generally these flashes worked pretty well. Some units would tilt and swivel the flash head while the sensor remained aimed at the target. This greatly reduced the working distance, but could give better modelling of the subject.
The "ultimate" auto flash was the TTL, or "through the lens" system. Used by the Pentax LX and some later "fancy" Pentax cameras, and IIRC the first Pentax DSLR, a sensor inside the camera measured the light falling on the film/sensor as the exposure occurred. I found that it worked wonderfully well on my LX.
Since your ME lacks the internal sensor you'll need a plain vanilla "auto" flash. It'd be a good idea, since the ME has an electronically timed shutter, to check
Photo Strobe Trigger Voltages to be sure you won't fry the shutter. I suspect any Pentax flash is safe to use.
As far as knowing whether your shots are properly exposed...experience and faith! If you can shoot a roll before the event and check the results you should be okay.
Good luck, and enjoy!