You won’t be using a traditional RAID with TrueNAS Scale. You have a choice of Stripe, Mirror, RAIDZ1, RAIDZ2, RAIDZ3, dRAID1, dRAID2, dRAID3. The docs are very detailed, so you should read up on RAIDZ and the other types elsewhere, too.

It has also improved a lot in the last years. PHP5 and especially versions older than that weren’t very good and deserved a lot of the criticism. PHP7 and onward are much better languages and don’t deserve the hate.

Since you only use Plex because of overseerr: There is a fork called Jellyseer that is compatible with Jellyfin. Haven’t tried it yet but it may be worth looking into.