What should I buy?

[Saltrams]

I have a 7004T that I'm very happy with and plan to keep. My problem is that every 2 years or less, I need to buy larger HDDs for the Vol1 Mirrored RAID, my latest order being for 2 x 14Tb discs. This leaves me with the smaller discs, which I move on down to be MyArchive 1 & 2 in the remaining bays. However, I am thus left with the smalles cast-off specialist NAS HDDs (I use Seagate Ironwolf) without any housing. I am about to have 3 such 4Tb discs.
Rather than litter my desk with external HDD enclosures, I'm wondering if I should get another Asustor NAS, hopefully 4 bay, to expand storage tidily and usefully. Would anyone recommend doing that & which model should I choose? I suppose that the 1004T is the most basic and would suit purpose?
Or is this a stupid and/or unworkable idea? Thanks for any advice.

[orion]

I think you can consider AS6004U which is a USB extension interface. Note: it's USB interface, so the bandwidth cannot compare with internal bays. You can create another RAID-5 volume (cannot combine with internal bays). In this way, you won't need to setup user accounts, apps, ...

[Saltrams]

Thank you Orion, I will check out the AS6004U availability & features.