Help me spend $$ on an M1 Mac Mini system.

[btfc]

Depending on speed, age, etc. you might drop the 2TB drives into something like this:

https://eshop.macsales.com/item/OWC/MED3ER0GB/

Of course, newer, larger HDDs are pretty affordable now.

Also, it sounds like you might benefit from some sort of hub; again, the sponsors are a good place to start.