Can I use a multiple-entry Schengen visa for business and tourism?
score:3
Accepted answer
You don't need a new visa if you didn't reach 90 days continuously and your visa is still valid.
You REALLY don't need to enter Germany first, but it's BETTER to do so. Because immigration clearance might be a bit easier, like they won't ask why you come and how long you will stay before you go to Germany.
Yes you can enter other countries, as long as the country accepts your visa.