I’ll be moving to Berlin in January, aber ich spreche nur Englisch und ich lerne Deutsch. Ich habe die EU-Staatsbürgerschaft und meine Frau kommt aus Berlin.
I am a senior front end dev who has experience leading teams
Some advice (some of it obvious if you've dont it before and not specific for Germany but maybe it's useful):
Have a profile on Linkedin and Xing, upload to sites like freelance.de and maybe to a bunch of agencies. Be ready to send a profile, listing as many projects as possible, i.e. different roles in a company could be separate projects. Make sure all relevant search terms (languages, frameworks, tools) appear for each project even if repetitive. English-only is ok in many places, German-speaking projects can be a little better though.
It's all through intermediaries, which means you can (and should) negotiate rates hard without worrying about burning bridges. No call with a recruiter that didn't go pleasantly ever led to anything so if it feels weird just hang up. Expect to be placed 3-6 months min, 2 years max in a project. Research a little on "Scheinselbständigkeit" but it's not a huge issue these days. If you want 100% remote it should be possible.
Good luck and welcome to Germany :-)
1. Just get a tax advisor who is fine speaking English with you. Just let him do everything in the beginning. Afterwards you can do more of that yourself. Try to be classified as Freiberuflich, not Gewerbetreibender. It helps if you have an engineering degree, but he can help you with that.
2. Do at least two gigs per year (Scheinselbstständigkeit).
3. Use HAYS and others to start it of.
4. Continue to learn German. Maybe do some German interview training or something to get in. There are teams working in English, but you will have an easier time overall.
You are required to have Health Insurance if you live in Germany, and for freelancers it is quite expensive(it will probably cost more per month than apartment rent). This can be a dealbreaker for people with limited financial resources who need some time to get their business off the ground.
However, if you don't want to be tied down, something like "Elternzeitvertretung" (aka jumping in for people on paternity/maternity leave) might be interesting for you.