A daimyō by definition has a realm of at least 10,000 koku. So looking at these smallest daimyōs:

The 1633 and 1649 military muster regulation combined stipulates that in time of war a daimyō of 10,000 koku provides 235 men, 10 mounted, 20 guns, 10 bow, 30 polearms, and 3 flags.

Sankin-kōtai numbers fluctuated, but the 1721 regulations stipulates that a 10k daimyō bring with him 3~4 mounted men, 20 foot, and 30 servants.

So at the minimum, he is required by law to employ 13 horsemen, 83 footmen, and 180~200 or so servants and other men, for about 300 total.

We know however that he usually had more. Daimyō were notorious for trying to one-up each other and impress commoners during their processions, despite frequent Bakufu orders to cut costs and stop bringing so many people. My pre-modern Japanese isn't so good, but if I read correctly the 1721 order is prefaced by telling daimyōs to stop bringing so many people, what if there's not enough people to call upon on emergency because they keep bringing so many. And of course, even in times of war, a daimyō can't supply everyone.

I would hazard to guess a 10k daimyō to have under him 2030 upper-class "warriors", about 150 lower class "warriors", and perhaps 300 to 400 other people under employment for 500600 total.