n26 bank account is your friend. it breaks the catch 22 of not having a bank account until you have an address, and not being able to get a rental contract without bank account! see through card is sweet too. in terms of moving to germany the things that tripped me up a bit were:
do not expect chip and pin, let alone contactless. always carry some cash! a few of my early rides were finished on an empty stomach as little shops would not let me buy much needed snax! (cash withdrawal are also not free)
you have to go to the local burgeramt and do your anmeldung within 2 weeks of moving to any new place. they often dont/wont speak english so worth getting a few phrases memorised. mostly if you at least try that is enough.
there are two different tax numbers, both sound similar but are not. steuernummer steueridentifikationsnummer. one is your personal ID and one is your tax code ( I THINK?!) but it tripped me up a bit when I was getting my first wages.
'Mitnehmen' means take-away. Super useful for coffees and late nite kebab adventures!
i have not been stopped for reflectors but I have also not actually had a run in with the bike police yet. i would deffo advise having two brakes though as they will stop you if they see you riding fixed. also, if you are that way inclined, 80€ on the spot fine for red lights. they will deffo not take daft forrin card for an excuse!
edit: i found sendbike very helpful and reliable for shipping, not just of bikes, and well worth giving them a call for good deals.