Cases or CaseProgress Customisation - Where and how to add a new field to be used in Cases, displayed in CaseStatusBox in combination with workflow?

Using Cases, in combination with Case workfow, CaseProgress and CaseStatusBox I am struggeling with the follwing questions?

- Which table and views should I add a custom field to, if it has to be displayed in the CaseStatusBox Screen and worked through
a customized Case workflow?

Thanks a lot for any help :-).