1. My visa was issued by a mission of another Schengen state. Can I use it to travel to Germany?
As a general rule you may cross any Schengen border with a visa issued by any Schengen country.
The Schengen visa has to be applied for through the Embassy of the country which is your main destination. The entry into and departure from the Schengen area can occur at any border crossing.
However, the short-stay visa does not automatically entitle you to enter the Schengen area.
At the border (or during other controls) you may have to show the visa but also provide additional documentation, for example information on your travel destination or that you have sufficient means to cover the stay and the return trip. It is therefore recommended that you carry with you copies of the documents which you presented when applying for the visa (e.g. letters of invitation, travel confirmations, other documents stating the purpose of your stay).