The official German customs website referenced in Noldor130884’s answer summarizes the legal stuff as follows:
If you are staying in Germany you can usually bring properties in your baggage into Germany at zero import duty and without customs formalities.
The most important restriction to this is
Goods that you bring to Germany and that you intend to leave (such as visitor’s gifts) may only be imported duty-free within the traveller’s allowances.
In my opinion, being a German citizen shouldn’t pose a problem here. If you were a German resident, there might be a problem if you tried to claim (without proof) that you were actually planning to take all the fancy stuff you brought with you, again.
Credit:stackoverflow.com‘