An easier to apply equation will be to determine how many planets, rogue objects and moons are easy to seed with frozen ocean vent life. Carbon sources and vents might enable insects. Ocean vents might need metals and some sort of barrier to keep out vacuum across a stadium volume. I'm looking at solid-state parts in micro reactors to model, but I'm also seeing the diversity of vitamins biology is capable of making. You would want to make weeds or toxin species that devour everything, so there is lower life seeding, and then stable eco-system seeding, assuming a few trailer loads of maintenance payloads there at the time of seeding.
The nicest life seems to be that able to signal with light it is ready for sexual meosis, but there might be something even more aesthetic possible.