Hello
I was recently granted a german National Visa type D. It is a visa to start working as an employee for a company that sponsored me. I requested a start date based on the estimated processing time, however it was issued in a record time. So the visa starting date is December 15 2017.
The company would like me to start working as soon as posible and if I knew the visa would be processed so fast I would have chosen an earlier starting date. So I have a few doubts
I am from a non UE country that doesn't require visa to enter Germany as a tourist, but it requires visa to work
Is the visa starting time only applicable as a starting date for work, could I arrive earlier to settle and find a place to live, given that I don't require visa to enter German soil. 
Is there any way that I can start working before the visa starting time, would it be illegal ?
In case is not possible to start working before the visa starting date, I would like to arrive to Germany earlier, as a tourist, if I do this, do I need to get out of Germany and then reenter with my working visa ? Is it any difference in the stamp I get at the immigration counter ? Can I change my status form tourist to worker after I have entered Germany

It would be of great help if someone could give me some advice about this

Thanks all !

Congratulations on your visa approval and welcome to Germany.

As for your query please do not and i repeat PLEASE DO NOT under any circumstances start your job before 15. December 2017 or apply for a tourist visa.

However, I may suggest to contact the embassy (by email or fax) and explain them your situation, they might be able to change the starting date to 1st of December 2017.

Good luck and keep us posted.

Best regards, RV++

P.S: this is not a legal advice!