How do I start an Multimember LLC (Partnership - 2 Members) with a friend who lives in a different country? And what will be our tax-situation?

My friend and I are passionate and dedicated about life-coaching and want to legally start a business. Although most of our business will take place online (coaching calls, later on we will start seminars and in-person coaching), we would use a virtual P.O. box in Sherman Oaks, CA as our business address. I am a U.S. Citizen, he is not (He is from Germany). I've read many times that he needs a Tax ID, but I've also read that he isn't taxed in the U.S. because LLCs have flow-through-taxation and it will count as income in Germany for him. How is it possible for us to start our LLC together as partners from different countries? What are challenges and hurdles that we have to go through? Thank you so much for your time!