Great setup. I built mine very similar except I went for the HBA back in 2019. I didn't want the motherboard controller to drive the reads/writes and sometimes the drivers don't work out of the box and you need to side load drivers for installation (from what I read) so I offloaded it to HBA which is on UnRaid support list.

This what I got. https://www.amazon.com/StorageTekPro-9211-8i-FreeNAS-unRAID-6Gbps/dp/B07JZ6FYVC

I then bought a 4x1 SATA cable that plugs into single port on the dual port HBA.

https://www.amazon.com/gp/product/B013G4EMH8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I was concerned about performance, especially when I run virtual machines along with the docker containers while having 9+ people streaming from my PMS at a time.

I actually bought spares of the card and cable, along with an additional hard drive as warranty replacements can take a few days from Seagate (great choice on drives btw). I haven't had any issues (knock on wood desk) other than hard drives going bad which just happens sometimes. Good news is Seagates warranty is fantastic.