Make a NAS of an old tower and various disks.

Hi,

I have an old Win10 pro tower that's used mainly as a file server.
Its various drives (1 x 230 GB SSD, 1 x 8 TB HD, 1 x 4 TB HD + 1 x external 8 TB HD used as backup) are fed to the teeth.
However I have various 5" 1/4 drives of various sizes sitting on my shelves (x 4 TB WD40EZRZ, 1 x 2 TB WD20EZRX, 1 x 2 TB Barracuda, 1 x 0.5 TB Barracuda)

I dream of turning this PC into a NAS, with some RAID-something redundancy. IIRC, normal RAID requires all disks to be the same size. But maybe in these days of awe, one could make something more optimised?

What would you suggest, harware and software-wise?