Check minidisc.org for MD deck info. I found yourrs there (
http://minidisc.org/part_Sony_MZ-EH1.html) and it will definitely
not take a mic directly. Whoever told you you could was wrong. It only has usb and headphone jacks. The only way to "record" with it would be to transfer audio from a computer to the MD deck via USB, in which case you might as well just use the computer to record the audio.
So you're out of luck trying to use that as a field recorder. Your idea of getting a JB3 sounds like a much better way to go.
When you get a JB3, you will need to connect a powered mic (usually mics + a battery box) to it as it doesn't have a real mic input that supplies power to the mics. If you just get the JB3 you could use it to be a patcher until you get some mics of your own.