The regular German tax lawyers can only do what they learned during their regular education...
I can "recommend" you "Flick, Gocke and Schaumburg". They have a very good lobbying team in
Germany ( a lot better than the big4) and also have an event every year where you (if your turnover is enough) can meet high ranked German officials who are directly involved in the process of making future tax laws.
Why "recommend" ? Because I fear big law firms. I once did a tax saving structure with KPMG and it was the worst decision ever... . Multiple people are able to access all your files, you get introduced to someone new every 4-6 months as someone leaves, goes to the competition or get a burn out, haha. That's why you frequently find the companies formed by staff from the big 4 in the luxleaks, paradise papers or wherever. And then they really black mail you if you want to change. They get money setting up your structure and then take your money for defending you in court.
The structures from them will work if you keep the money IN the companies and don't spend it for yourself. But you won't come around
income tax (even for "Geldwerter Vorteil") if you continue living in Germany. 0% tax is legally only possible by relocating your whole center of life to a
tax haven or becoming a PT with a moving center of life.
However, maybe it is enough for you to keep money in your company to grow faster and regularly pay your personal tax and do as much as possible as company expenses. You will be limited and need to collect receipts/do accounting, but maybe this is ok for you.
And also keep in mind: After Wirecard there may be some law changes incoming in Germany which will limit the abilities of companies like the Big4 and FGS etc.