Use your Visa or Mastercard for most transactions....ATMs do not penalise you that heavily for withdrawing cash. I would have thought 250 equivalent in notes for casual cash and check if your hotel has a safe in the room.
Bear in mind that if you're a pensioner public transport is free in the city - buses, trams, underground, the lot. No ID to buy, in two visits were stopped once (by a very friendly man) who was quite happy once he'd seen our passport or driving licence (I can't remember which).
depends if you want to pay for meals or accommodation with cash. I'd do as DTC suggests and pay with a credit card wherever possible. (There are a couple available that do not charge commission on paying for things abroad.) Then figure out what small things you're likely to buy - lunch maybe, small souvenirs, the occasional beer?