A correction: it is the USB-C (USB3.1 gen2) Dual Drive Bay dock. I connect it to Mac mini's Thunderbolt USB-C connector (I try to study and use the correct USB-C / Thunderbolt nomeclature but it is still messy...). But I do like them because it has greatly reduced the rat's nest of wires under my desk.
I got the fastest CPU because I do photos and video and just to be future proof (I tend to buy expensive and use the gear for a long time).
I got 16 GB RAM because some reports suggested 8 GB might not be enough for smooth display. I have experience installing RAM and storage so I could have saved some money by installing cheaper RAM myself but some cheap suboptimal RAM might produce obscure errors so I didn't do it on such a new Mac, maybe later.
I got 1 TB HD because according to MacInTouch forum that is faster than smaller drives (*) and I do video work that needs HD space.
(*) Sequential write performance between the SSD sizes in the Mini:
128GB -> ~0.6 GB/s
256GB -> ~1.3 GB/s
512GB -> ~1.9 GB/s
1TB -> ~2.6 GB/s
Reads are all > 2 GB/s.
I also got 10 Gigabit Ethernet option although I might never need that. That might be useful when moving large video files between computers although currently I use HD docks for that.
https://eshop.macsales.com/item/OWC/TCDRVDCK/