Hi there

General rule is that you have to pay taxes for everything crypto profit that is sold inside one year after purchasing - with a tax exemption limit of 600,- Euro. It doesn't matter, if you exchange into other crypto or fiat. If you hold your crypto for more than a year and sell then, there are no taxes. Since you have your XRP since 2018, I wouldn't worry with anything regarding taxes, if selling while in Germany.

This also makes the rest of your questions obsolete, which couldn't have been answered very easily anyway (at least by me ). Would have depended on a lot of other things (duration of stay, if you work here or just travel around etc.)