Advice on going self-employed / contractor in Germany?

Hello all! I've been a Software Developer for almost 15 years now, and after staying at my last few companies for only 2 years each, I'm starting to think about the possibility of becoming a freelancer/contractor. I'm looking for more flexibility in my work and getting out of parts of the corporate culture that I have grown to dislike.

I'm in a good place financially, and so I'm looking to see if it's a possibility. I speak English and German fluently, and have primarily a background in webservice and FE development, though I can also do quite a bit of Rust and have dabbled in Android apps a bit. I also have some experience with medical software. I think my biggest issues right now are business model development / pricing and finding customers.

Does anyone know of any good resources? I find quite a bit online, but a lot seems geared towards being self-employed generally, and not to the software industry itself. I'd be looking for either good websites or books, or general starting points for research.

Thanks in advance for any suggestions or advice!