I have my retirement accounts from back when I was still living in the US, but I cannot add to them.

Anything I make on a non-retirement account has to be reported to the German tax authorities, too - and I'll probably have to pay German taxes on those gains when I pull money out of them. Germany taxes all income earned by its residents, no matter where the source, but if my husband (German citizen) were a US resident, they would not tax what he earned in the US.