The dull parts of a long trip cause the most stress when you ignore them, and the least once they are sorted. An afternoon of admin before you go buys you weeks of not worrying.
For phones, an eSIM is the simplest answer now. You buy a European data plan online before you leave, and your phone connects the moment you land. Keep your home number active so the bank texts still reach you. For money, tell your bank your travel dates so the card does not get blocked, carry two cards from different networks in case one is refused, and when a machine offers to charge you in dollars, always choose the local currency instead.
Sort the paperwork while you are still at home and calm. Travel insurance that covers your full trip length and any existing conditions, a check that your passport has enough months left on it, and prescriptions filled for the whole journey with a copy of the doctor's note. Keep digital copies of all of it somewhere you can reach from your phone.
None of this is exciting, which is exactly why it is worth doing early. Get it out of the way in one sitting, and the trip itself stays light.