I saw that you can keep some minerals, and even buy some if you want. Why do you need minerals for anything other than selling for money?

you need them to build things. the higher the level the more expensive the mineral required to construct it

You need them to build on planets and ships, or what? I must not be high enough level to experience this.

both. you dont need a lot, mostly its credits you need to build but you also need some minerals. you could just buy what you need or you could keep that type of mineral you need when you go to build. for planets you need it for structures and among others, for ships you need it to build modules. modules are like components of an audio system. weapons, shields, defense, scanners, energy and cloaking plus other things.

Yes, beyond the 1st research tiers almost everything costs minerals to build. They also become your primary source of money, much more than missions.

Minerals
1) Source of money
2) Sending "money" to legions
3) Used in constructing modules/structures (You will understand this better once you have something that needs minerals)
4) Used for some missions



IT is not related to level. It is related to research. Once you unlock the better modules/structures they need those minerals. Some items may need items from "special tab" though.

Question: Why not I just buy them when I need them?
Answer: Selling off minerals has a 20% tariff. So buying them back will cause a loss of 20%.

Q: So should I stock up on my minerals in my cargo?
A: Better not if possible, it might be raided (stolen)