within euro zone, you would not need any other bank. pay for free with german credit cards allover €-land, ATMs are easyv - even in smaller places. HSBC doesn't have a very large network, so eventually, you'll have to deal with (in Germany sometimes hefty) ATM fees, charged by your bank.

Sparkasse has one of the best network in Germany - thatīs what I'd use. Escpecially HaSpa - Hamburg Sparkasse ranks among the best banks in Germany.