You should talk to a CPA about this issue. The US should give you a foreign tax credit and Germany may also give you a credit. I would check with a german accountant. I hope this answers your question. Thank you.

You should talk to a CPA about this issue. The US should give you a foreign tax credit and Germany may also give you a credit. I would check with a german accountant. I hope this answers your question. Thank you.

It's a progressive tax system, the more you make, the higher tax bracket you'll be in..

It's no different than anyone with more than one income source. You don't file a return for each source, they're all combined one one return, it could be a single person with two jobs, or a married couple with each having one job.

You're right,of course, the tax on a pension of 20,000 will be less than someone who has a $40,000 salary from a job, who in turn will pay less than someone with a combined income of $60,000 who has both. It's simply how progressive taxes work.