You don't mention specifics on the crafting chain this mod introduces. I'm wondering what the recipe chain is.

I was thinking about doing this very thing as I hate the "ship wide belt of asteroids" solution and wanted something more in line with "The Factory Must Grow". A giant processing plant is just the thing I want!

So looking at the recipes, a couple of them would flat out require the mass launching of barrels. Using holmium solution and fluorine makes this tough.

Have you played with it at length to test the balance?

I'd replace holmium solution ingredient with the plate (as the catalyst, because science!)
Not sure what to use in place of fluorine, my instinct is to require 10 fluroketone cold, giving back 10 hot, making it a closed loop but requiring a cooling setup.

If you wanted to test with the changes I mentioned I made a version with the alternate balance:
https://mods.factorio.com/mod/fg-promethium-processing

The holmium plate idea is a pretty good one, ill implement it in a few minutes. As for the fluorine, that's really only there because i wanted to give another use to fluorine aside from making fluoroketone, mass launching barrels is pretty annoying so ill switch it to cold fluoroketone.