At least a few hundred billion bodies can be in a stable orbit without the majority of the system mass at the center. Our own Milky Way Galaxy is in a stable orbit with hundreds of billions of bodies. The black hole at the center of our galaxy, Sagittarious A*, is estimated to have a mass of only $2.6*10^6_\odot$, while the entire Milky Way has a mass of about $1.5*10^{12}_\odot$. So, while the mass of the black hole is substantial, it isn't a substantial part of the overall mass of our galaxy.

In fact, the spiral structure of the Milky Way is driven more by gravitational interactions between the stars, rather than interactions with the black hole center.

From Baba et al.:

The spiral arms of disk galaxies are the most prominent structures, and the arms are formed due to gravitationally driven variations in the surface density in the stellar disk

Michikoshi and Kokubo 2020 perform N-Body simulations of galactic spiral arms with N = 4000 stars.

At least a few hundred billion bodies can be in a stable orbit without the majority of the system mass at the center. Our own Milky Way Galaxy is in a stable orbit with hundreds of billions of bodies. The black hole at the center of our galaxy, Sagittarious A*, is estimated to have a mass of only $2.6 \times 10^6 M_\odot$, while the entire Milky Way has a mass of about $1.5 \times 10^{12} M_\odot$. So, while the mass of the black hole is substantial, it isn't a substantial part of the overall mass of our galaxy.

In fact, the spiral structure of the Milky Way is driven more by gravitational interactions between the stars, rather than interactions with the black hole center.

From Baba et al.:

The spiral arms of disk galaxies are the most prominent structures, and the arms are formed due to gravitationally driven variations in the surface density in the stellar disk

Michikoshi and Kokubo 2020 perform N-Body simulations of galactic spiral arms with N = 4000 stars.