I'd take a recommendation from Ted as a pretty convincing endorsement!

Note that most mixers have phantom power but unless it's a very expensive mixer you have to turn phantom on or off for all channels at once. Not usually a problem but watch out for other inputs with jack-XLR converters or DI boxes that can't handle P48 (stupid design but it happens).

I use a Microvox mic built in to the bass end of my melodeon, and a Shure SM57 on a stand for the treble side. I made a special battery box/mixer to power the Microvox and combine the two signals.

Also: "One melodeon is about the equivalent of 4 fiddles. Do you need to amplify at all in medium sized venues? "

Absolutely yes, unless you know exactly where you are going and what sort of event it is. Even 50 melodeons are no match at all for a room full of excited and tanked up wedding guests or (to recall a recent example for me) students after a boat club dinner. Amplification requirements are mostly not about room size (unless it's *very* small) they are about competing with background noise.