I'm guessing he is holding back because he knows that the most capable will be pressured into government service which will hinder his Dungeon Buster business. Also if he's a civilian that is shown to have capabilities that could only be acquired in the dungeons, he'll be investigated and his personal dungeon and the fact that his entry triggered the other dungeons would be revealed.
I thought he was going to lead his own crew. No sense in acting weak if that's the case.
More likely than not, he's trying not to stand out, so people don't find out he has a secret training dungeon that he's controlling, that literally drops Money. That would be a big no no to any government. The story kind of hand waves it away, but if the government is as strict as the story implies, just randomly injecting 100M Yen, won't show up too easily, but that will start being a real problem once other dungeons that drop money are discovered. At least with other stories, it's "coins" or actual materials, Magical Currency Inflation would make most governments set up check points and guards at all the dungeons that drop it.
He is forming his own team, so he's also participating to scout potential members. Like obviously, if they're giving this new kid this much screen time, he's going to join. (They already foreshadowed this and who the members will be in earlier chapters. Ch7 pg 30-31, though Ishihara is obviously now going to be a government liaison.)
Yeah, that happens in Chapter 7, he hands 100M off to someone to money launder through crypto money exchanges. I'm saying that it's not a long term answer. 100M of actual currency isn't that huge in such a big economy. But once you have tons of people doing it, and you have lots more money floating around than the government actually printed, it starts becoming a problem. Other stories make this not a problem, by dropping fictional money.He did some money laundering in the LN, if I'm remember correctly