Using FBA (Fulfillment by Amazon) you should work together with an experienced tax consultant. FBA means that Amazon takes care of as much as you would like. You could start with using a warehouse provided by Amazon. You would deliver your goods to this warehouse and whenever you sell something this is taken out of the warehouse.
The VAT consequences differ in Germany to other EU countries. In Germany you will have two VAT steps. Step one is the delivery to the warehouse (e. g. an intra Community movement and acquisition). Step two is the sale, which would be taxable with 7% or 19% when the goods go to a place in Germany.
Just using a warehouse of Amazon will not create a permanent establishment (PE). This means that you will not be applicable to German income tax and you do not have to file any German income tax declarations. However, you will have to file the monthly VAT statements and the yearly VAT declaration and in case of exports to other EU countries the summary statements and may be the statistics (destatis).
Amazon also offers to take care of the shipments and returns. However, you will still be the seller and you will have to take care of the VAT. Usually, you would need to book each sale separately because from a civil law perspective each sale is one legal transaction. However, with thousands of lower-amount-sales, this requirement would be disproportional. We can find a solution together with the tax office. From my point of view it should be sufficient to make two bookings per day whenever you receive the payment from Amazon (booking the turnover and booking the Amazon fees). You would of course still need to document your sales but these types of lists can be created out of Amazon.