Char Based ATP check in MTS scenario

Hi,

I am aware that in case of MTO (Make to Order) scenario, variant class (300) is required along with batch class (023).

I have following query for char based ATP check in MTS scenario --

If variant class is not part of the scenario, how the characteristic values are entered in sales order?

How does the ATP check takes place in this case i.e. char. matching ?

Which class will be present in APO product master?

Is IS-MILL activation necessary if I want to consider chars only in ATP check and not in forecasting and production planning.

What are the other relevant settings for MTS scenario?

Thanks in advance,

YR