score:3
With your multiple-entry visa you can come and go in the Schengen Area as many times as you like. Just make sure that you do not spend more than 90 days in total in the Schengen Area and that you do not stay beyond the validity period.
Your visa type D is valid for Germany, but allows for visits to the other Schengen States, with the possible exception of Spain, that does not recognise Kosovo as an independent state. You can therefore transit trough several countries without an additional visa. While not in the Schengen Area yet, Croatia will also accept your German visa.
Bosnia-Herzegovina will require a specific visa and Serbia will not accept a Kosovan passport.