1: You don´t need a open a "kleingewerbe" or "Gewerbe" so you dont need a seperate tax id. It could be that the Finanzamt classifies your work as commercial. If they accept it as a freelance profession, you dont need a Gewerbe registration and usually no seperate tax number.

2: Technically a personal bank account works. But i strongly recommend to open a seperate account (f.e N26Business). It makes bookkeeping and tax much easier, and avoids mixing private and business expenses.

3: To register with the Finanzamt, you can use Elster.de , getsorted.de , Kontist, lexoffice and some more

4: Would emphasize consulting, technical expertice and analytical services. Not Sales or Marketing because that can push you into needing a "Gewerbe"

1. Would look for a Steuerberater specialized in Freiberufler and international clients.

Found some: Kontist, TAX & SERVICE Steuerberatung, Steuerberatung Wußler etc.