Some good workholding info on this thread. I 3D print blocks and fixtures and I might adapt the Datum plate and MiteeBite design for my A4 mill which I mainly use for acrylic cutting.

My mill is in sort of storage at the moment as I am refitting my den during lockdown. I have plans to modify the mill to make the steppers more 'inboard' and change the homes and limits to travelling switches on X and Y. I am photographing it so there may be a thread about it later on.