New Mill losing steps

[EddyCurrent]

With encoders you get feedback so things like missing steps should not happen. Many people use just stepper motors without feedback and they work fine, but only when everything else is right. If your machine is not working right, as you are saying, then I would suggest the reason needs to found before thinking about fitting encoders otherwise you would probably just be wasting money.
I think you need to getting it working as it is first then you might decide it's good enough without encoders. I don't know why you didn't follow through with the free advice here.