Resize array: https://m.youtube.com/watch?v=nV5snitWrBk

Yes you will likely have to rebuild parity. If its write once read many kind of media (for the array) zfs is a lot of overhead and learning. Z snapshots and data sets are possible with a zfs plugin. https://m.youtube.com/watch?v=pLFaDnTVpuM

Cache drive in unraid is used as temp storage before being put in the array. You don’t need a slog.

Unraid is not turenas or proxmox. Tis a different beast you sound like your trying to plan a system that would belong in truenas.

Dudes government shot a kid and it’s the video games fault………good luck on the reelection

I found it so hard to get through the Elfen Lied anime. It was the glacial pace for me more than anything else.

When you say weak, what do you mean? Never seen it but might add it to my watch list.