How much grunt do I need to run 2-3 simultaneous high bitrate 4k streams?

[Efficient_Good_5784]

* If I build a raid array, with some level of redundancy, can I say for example have like 4 16gb iron wolf pros, with 1 of them as redundancy? Can I add in hard drives to that array later on to expand it?

If you use ZFS and configure as a RAIDZ1, you can just keeping add hard drives to the pool and it will accommodate them.

Responding more-so to OP's question here since you brought up ZFS.

Talking specifically about OpenZFS, RAIDZ expansion is supposed to be supported starting with OpenZFS v2.3.
If you're using an older version than that, you can't expand any RAIDZ array. Those remain permanent with the amount of drives they contain once they're created in older versions.

You can always add another VDEV to a storage pool in ZFS. RAID is not at the pool level, but at the VDEV level in ZFS.

The minimum drive count for RAIDZ1 is 3 drives (2 usable, 1 parity). That means, if you want to expand a pool that already has a RAIDZ1 VDEV, you'll need a minimum of 3 drives to add another RAIDZ1 VDEV. Though with two RAIDZ1 VDEVs, you'll lose 2 drive's worth of space to parity.

I don't know when OpenZFS v2.3 is set to release, but until then, this is a limitation of ZFS's RAIDZ.