Korach had "250" on his side. How many did Moshe/Aharon have on their side?
What do the rabbis say?
Rashi on Bamidbar 16:19:
ויקהל עליהם קרח. בְּדִבְרֵי לֵצָנוּת, כָּל הַלַּיְלָה הַהוּא הָלַךְ אֵצֶל הַשְּׁבָטִים וּפִתָּה אוֹתָם — "כִּסְבוּרִין אַתֶּם שֶׁעָלַי לְבַדִּי אֲנִי מַקְפִּיד? אֵינִי מַקְפִּיד אֶלָּא בִּשְׁבִיל כֻּלְּכֶם, אֵלּוּ בָאִין וְנוֹטְלִין כָּל הַגְּדֻלּוֹת, לוֹ הַמַּלְכוּת וּלְאָחִיו הַכְּהֻנָּה" עַד שֶׁנִּתְפַּתּוּ כֻלָּם
ויקהל עליהם קרח AND KORAH CONVENED [ALL THE CONGREGATION] AGAINST THEM, by means of scoffing language: that whole night he went round to all the tribes and tried to win them over: “Do you really think that I care for myself alone? It is only for all of you that I have a care! These men come and occupy every high office: royal rank for himself, for his brother the priesthood!” — until in the end all of them submitted to his persuasion (Midrash Tanchuma, Korach 7).
(Quote and translation from sefaria)
It seems from here that moshe had very few, if any, followers by that point. Korach however seems to have quite a following, though the 250 were likely the most outspoken, seeing as they spontaneously combusted.
Based on the Pasuk in parshat Korach Bamidbar 16:25, Moshe went to Datan & Aviram with the Elders of Israel. A simple read of this verse means that the Elders were on Moshe's side.
Ibn Ezra says the Elders of Israel were 70 chosen people (based on what happened end of Parshat Behaalotecha since Ibn Ezra holds that the Korach rebellion happened in Chatserot, before the sin of the spies). Rabbeinu Bachya holds pretty much the same position.
Bechor Shor says the Elders of Israel were with Moshe to show him honor/repect.
