Astro Beans, Dwarf Fortress-like Game

I want to make a Dwarf Fortress-like game. I would like to make some asteroids for my astro-beans to mine and build habitats inside.

Specifications

Procedural generation so I can use the same seed to recreate the same conditions

About 4 million space rocks or gravel piles more than 1 km across

The main belt is 2 AU wide at 2.8 AU, from 1.8 to 3.8

There are roughly 5 asteroids at least 1 km across per million square kilometers

The 520 square window is out to Jupiter @ 5.2 AU, 50 px/AU, so each pixel is 3 m. km across

Zoom in on 3 m. km inside of 520, make that 5.2 m. km across and 10^4 km/pixel

Instead of checking each pixel, check a grid of 52 10x10 pixel boxes, 5 divided by 10^2 is a 5% chance per grid box

(I probably need to reconsider this positional bit; check out how crippling 4 million objects would be...)