Next you find an accountant. But payroll setup, health insurance setup, accident insurance (required in Germany but very cheap), local tax, VAT tax setup can wait. You're not really allowed to use the 25k to pay your own salary anyway, only business expenses. Expect ongoing 500-1000 Euro/month for a GmbH accountant.
It's easier to set up a UK Ltd or an Estonian entity but there will be all sorts of tax implications.
For any Atlas-related follow-up questions, don't hesitate to reach out: julianlehr [AT] stripe -- happy to help :)
I am running one platform in that space (www.firma.de/en/). Feel free to reach out via ck AT firma DOT de and I am happy to jump on a zoom call. There are surely more things to cover.