"...וְשַׂמְתָּ עֲלֵהֶם שָׂרֵי אֲלָפִים שָׂרֵי מֵאוֹת שָׂרֵי חֲמִשִּׁים וְשָׂרֵי עֲשָׂרֹת׃ וְשָׁפְטוּ אֶת־הָעָם בְּכָל־עֵת ..."
"Set these over them as chiefs of thousands, hundreds, fifties, and tens, and let them judge the people at all times. Have them bring every major dispute to you, but let them decide every minor dispute themselves."
According to the existing Halachah we set up 3 different forms of Beis Din - 71 and 23 for criminal and of 3 for monetary offences. There's is an option for דן יחידי but it is not encouraged.
THe question is how those 78,000 judges were arranged in courts:
- were they all דן יחידי?
- were they grouped in courts of 3 or 23?
- was each one establishing a court by joining two laymen to be 3?