Ideal 2-4 bay HDD Enclosure, for MSI Cubi 5 home/media server

Howdy!

Currently running an MSI Cubi 5 with the following:

• Western Digital WD Red Plus 8TB 3.5" NAS HDD, WD80EFPX
• Seagate 1TB Desktop HDD [exact specs unclear]
• Seagate 1TB SDD [exact specs unclear, currently acting as Cache pool device]

Likely going to upgrade my MSI Cubi 5 with the following:

• Crucial CT16G4SFRA32A 16GB (1x16GB) PC4-25600 (3200MHz) DDR4 SODIMM
• Crucial P3 Plus 500GB M.2 2280 NVMe PCIe 4.0 SSD

Considering one of the following options to replace the Seagates/increase storage, which is where the HDD bay hunt comes in:

1. Western Digital WD 6TB Red Plus 3.5 inch SATA HDD, WD60EFPX [considering 2 if I can justify the price]

2. Western Digital WD Red Plus 8TB 3.5" NAS HDD, WD80EFPX

Hardware is not my strong suite so I'm having trouble figuring out the best enclosure/bay option for the HDD. Ideally I'd like to keep costs low, but am hesitant about refurbished unless from a trusted source (I don't know enough to vet items myself). Would love some suggestions, bonus points if you know its available in Australia.

I'm also open to hearing alternative solutions for all of the above. I'm still in the midst of doing my own research so the plan is in its early days.

TIA!