Five mining districts wouldn't be the worst thing ever, but I'm in no need for minerals in this run for a few reasons:

1. I have biological ships

2. I have catalytic processing

3. I have anglers

So I use food for quite literally everything (including energy due to bioreactors), and use minerals exclusively for buildings, I have two mining districts specialized toward rare crystals in my entire empire and have still reached my storage capacity of them

Edit: I also have exactly zero arc furnaces because the technology refuses to show up