Hi there,
You can not have both item or overall working all together. You need to decide whether you will release item by item (then no classification but release procedure criteria are limited to plant, accnt assignmt, mat grp and value). No classification.
Procedure with classification offers much more options but it's a release for the overall doc (complete release or not). Work around would be to create PR for each requirements.so you'll release one by one 
.
Note that classification is not link to doc type.
Cheers !