I don't believe you have a "contract" to work freelance. You have an offer from a company needing your services- as a freelancer. A contracted employee in Germany needs a work contract, which includes payment of taxes, contribution to the social system, health benefits, etc. If someone is offering you a contracted position, they are offering you a job, you will work for them and only them, and for this, you need a work permit- which is extremely difficult to get if you are not from the EU or in a specialized field in need in Germany.
To accept work as a freelancer you need a residence permit with permission to work freelance in a designated field. You get this permission from the Aliens office ("Auslanderbehoerde") when you apply for a residence permit. Since you already have a residence permit, I am not sure if you go to the Arbeitsamt or the Aliens office. I think you need to go to the Aliens office and have your current stay permit 'converted' or 'ammended' to include the permission to work as a self-employed person.
I came to Germany initially on a one year language study visa. After my one year (and having moved jurisdictions), I went to the Aliens office (in my new jurisdiction) and had my permit extended and converted in one procedure.
You probably only need the letters from potential employers (well, technically 'clients'). You should have more than one potential employer/client/letter because technically, if you are only working for one employer, the official could deny your application for self employment based on the fact that you only have one source of income and thus should be hired as a regular 'contracted' employee- including benefits, taxes, etc. Then you're back to needing a work permit- which you need from the employment office ("Arbeitsamt"). Well, actually, the employer has to post the job opening there to make sure there is no 1) German 2) EU citizen 3) EAA citizen 4) Australian 5) American and other (in roughly that order) who is qualified/available to do that job. After posted for several weeks you will get permission from the Aliens' office to accept the job- and get a residence permit with permission to work stuck in your passport.
I applied for a study visa conversion/extention to freelance as an English teacher.
This is what I needed:
- passport
- city regristration ("Anmeldung")
- rental agreement (and a letter from the landlord that you are allowed to live there if your name is not on the rental agreement)
- proof of
health insurance- letters from 2 or more potential employers (including hours and earnings expected per month)
optional/may need:
documents which state your qualifications- I didn't need this, but if you've got 'em, take 'um. I took everything but the kitchen sink, just in case. I find that German officials love paper work and official looking documents. I had a binder full of documents- full of high school report cards, diplomas, etc.
(the last poster: since you live here with your husband, your permission will not be based on the amount you make. And now that I think of it, I believe there is some kind of exception for partners married to someone who is working here, allowing you to work part time (20 hours/week? ie. 400 EUR job) without permission of any kind. These jobs aren't taxed, etc. So if you aren't working a lot you might not need anything. If you are going to be making any substiantial kind of income you probably need the permission.
You will not receive a tax ID number unless you go to the tax office ("Finanzamt") and request one. You don't need a work permit to request a tax ID number. You call or go there and request one. They give/send one to you. The finanzamt isn't connected to the Aliens office- nor to the employment office- unless, of course, they want to be (to investigate or whatever). I have been working freelance for over a year and since I have not filed any taxes (yet), I do not have a tax number (yet).. I will get one when I file later this year.
I hope this helps.
((To the other guy who needs a place to stay but can't get a rental agreement without a job, the catch22: you could move into a WG ("Wohngemeinschaft"; ie. rent a room), just to get all your paperwork started, and then find a place of your own later or offer a couple months rent plus deposit and explain your situation...just a suggestion))
Best regards,
Jennifer in Frankfurt