Dear Nivedita,
1.presently there is no provision to check the data in draft mode,but you can compare the data model both in active and inactive versions.
2.Yes,you can add the button to UI application.
3.yes you can do customize search,refere to below link.
http://help.sap.com/erp_mdg_addon61/helpdata/en/9b/5b832e5b3e4ba7a764534774af7ba9/content.htm
Regards
shankar