There is no such DTA between Seychelles and Germany. If there was, you would probably have to go live there in order to be eligible any benefits.
I think both give you problems. Seychelles a bit more as you probably won't even get good banking.
You first need to figure out how many weeks you want to︀ spend in Germany and then where you spend the rest. You can then let me︁ know for good adivce. But spending 5 months in Germany will only lead to the︂ advice to either leave completely or pay taxes there. You may not get caught, but︃ that is not part of an advice.
I think both give you problems. Seychelles a bit more as you probably won't even get good banking.
You first need to figure out how many weeks you want to︀ spend in Germany and then where you spend the rest. You can then let me︁ know for good adivce. But spending 5 months in Germany will only lead to the︂ advice to either leave completely or pay taxes there. You may not get caught, but︃ that is not part of an advice.