Hi Novik,
Sorry it's taken me this long to finally reply, been quite busy lately.
The process of opening an international account at Charles Schwab wasn't too difficult/complicated, but it took a few weeks:
They have an application form (pdf file) on their website that I filled out and mailed in. Eventually they e-mailed me to set up a "Due Diligence Compliance" interview; it is a phone interview conducted with one of their representatives where they ask how much money one plans to initially invest, where the money is coming from (inheritance, salary, etc.), and a few other questions they seem legally bound to ask (to prevent laundering, etc.). After that, I received a confirmation that my account was open and how to set-up a user account for their website. To set up a user account I had to call and have one of their representatives guide me through the process which was somewhat odd compared to being able to set up the account myself, but whatever. And I received some mail from them in the meantime, but nothing crazy.
After making sure I properly filled out my wire-transfer form for my bank and sending it off (it is odd ordering an international wire-transfer to transfer money to the local account they offer, but Schwab requires that form of transfer since the money will be credited in the US), I am crossing my fingers everything works out well and the money gets to where it needs to go. I can keep you updated when things progress along far enough.
As for the tax side of things: I will receive the required tax documents and forward them on to my tax-professional/aunt when she files for me in the US. In Germany I'm just going to include the realized capital gains from my holdings with Schwab. It worked for my other capital gains last year and they didn't request any further documentation.
Hope this helps!
Cheers,
Bryan