You will likely only need a plug adapter. What kind of electronics are you taking? Most phones, tablets, laptops are built for 110-240 so all you need to do is have an adapter to plug them in to the socket.
IF you are taking something like a Blow dryer or curling iron, that's when you might have problems. Some of these you can buy that will be able to switch between voltage.
Tell us more about your electronics and you can get better advice.
In general, you will NOT need a voltage converter.
As to cash, the last trip for 5.5 weeks I used cash only at the little ice cream kiosks at the English seaside. Everywhere else I tapped my CC OR used Applepay. I even used ApplePay to access the toilets in the Amsterdam Centraal station. I had change but I did it because I could, lol.
DON'T take Dollars to change in to local currency. Get it out of an ATM. You'll need to notify your bank that you are traveling. Check your CCs as you may or may not have to notify them of your plans. Currently both my CCs I take on trips do not require travel notifications.