As I have limited space I was also looking for the smallest system possible for
Blue Iris during my search for a storage device ( NVR, VMS .. )
This is what I concluded:
Ideally get a system which can hold at least
ONE 3.5" SATA HDD and one
OS SSD/HDD ( 2.5" SSD or M.2 SSD works well on that )
Also a non-laptop i5/i7 CPU 4th gen+
The smallest systems which appeared at reasonable price points for performance was
used Dell and HP business class
SFF form factor systems.
If I wanted, I could build a nice custom small box with a i5/i7 that can hold a 3.5" - however that would run significantly more $