Help with Pool Configuration - Number of Pools, File Systems, and What to Use them For

I am about to rebuild my server, and I am looking for guidance on how to best utilise my drives and configure my pools. I can fit 20 drives in my case, and I have picked the most useful 20 I have.

This is what I'm currently planning, but not set in stone.

Main Array (xfs)

5 x WD Red 26TB (one of these as parity)

2 x Seagate Ironwolf 12TB

2 x Hitachi Deskstar 8TB

1 x Seagate Ironwolf 8TB

1 x Seagate Barracuda 4TB

Appdata (btrfs)

2 x Samsung 970 Evo Plus 500GB in Raid 1 (mirror)

The above is how my current server is configured, except without the WD Red drives, and the appdata pool is also used as cache for the main array. Since it is only 500GB though, the Samsung 970s often fill up when I download a lot in a short space of time.

With the new build, I will have much more space and ports for drives, so I was thinking of adding a few other pools.

Cache pool (btrfs??)

2 x Intel D3-S4510 960GB SSD in RAID 0 or JBOD

Having 2TB just for cache should stop the appdata drives from filling up with downloads.

Other SSD Pool (ZFS??)

4 x Intel D3-S4510 480GB SSD

1 x Intel DC S3510 240GB SSD

My best idea so far with these drives is to use them as storage for data that would benefit from increased speed. I'm thinking maybe Photos for Immich, Nextcloud files, Paperless documents. Having said that, I currently don't have any speed complaints with Nextcloud or paperless (they are just simple documents after all), and I haven't deployed Immich yet so I'm not sure how much SSD speed will matter there. Currently my Nextcloud files are 311GB and my photos are 430GB.

Since this would be important data, I would set it up with some sort of parity protected array or RAID config and maybe ZFS to help protect it.

I do run a lot of containers (76) but the only other one I can think that might benefit from fast storage is frigate. Not sure if that's a better use case than the above.

I also plan to do Plex transcoding in RAM.

So how does this plan sound? Any obvious mistakes, or better file system/RAID choices?

Do you have any other suggestions on what I should use the SSDs for, or a better way to configure all these drives?

The drives that didn't make the cut were a 2TB Seagate Barracuda Green, a 1TB WD HDD, and another Intel DC S3510 240GB SSD. I figured adding a few faster SSDs would be more useful than 3TB of extra HDD space.