Working in Berlin

Hello,

I'm from Belgium and will be moving shortly to Berlin to live there for a year. During this year my first residence will stay in Belgium and I will stay at my girlfriends appartment in Berlin.

I would like to know what I have to register for when I would be working a) a mini-job or b) a full time job in Berlin.

Do I need to register a second living place in the town hall?
Do I need to register with a health security company?
Do I need a bankaccount with a german bank in my name or can I use a bankaccount of my girlfriend for putting my salary on?
Anything else I didn't think about?

My girlfriend allready asked around a bit but it seems nobody is completely certain because of my specific situation that my first residence stays in Belgium.

So I hope someone here might have some answers.
Thank you in advance.

Sincerely,
Kurt Groeneboer